full page fax print - the partnership

Acknowledgements

From the outset, the production of this Guidebook has been a cooperative project involving several agencies and local governments who are challenging traditional stormwatermanagement practices in British Columbia. The Project Steering Committee included: Peter Law (project manager), Laura Maclean, Chris Jenkins, Helene Roberge, Eric Bonham,John Finnie, Sean DePol and Brigid Reynolds.

The primary authors of the document are: Kim A. Stephens M.Eng., P.Eng. (CH2M Hill Canada Ltd.), Patrick Graham B.A.Sc., M.R.M. (CH2M Hill Canada Ltd.) andDavid Reid B.C.S.L.A. Landscape Architect, Planner (Lanarc Consultants).

We wish to acknowledge financial support from the following organizations; B.C. Ministry of Community, Aboriginal and Women’s Services, Municipal Engineering Section;B.C. Ministry of Water, Land and Air Protection, Environmental Stewardship Division, Biodiversity Branch and Vancouver Island Region; Environment Canada through theGeorgia Basin Ecosystem Initiative and the Regional District of Nanaimo.

We also wish to thank the Project Advisory Committee who reviewed and contributed to various drafts of this document: Megan Sterling and Melody Farrell, Department ofFisheries and Oceans; Ted van der Gulik, Ministry of Agriculture, Fisheries and Food; Graham Savage, City of Nanaimo; Gary O’Rourke, City of Parksville; Bob Weir, Town ofQualicum Beach; Bob Cook, Ministry of Sustainable Resource Management; and Erik Karlsen, Ministry of Community, Aboriginal and Women Services.

Appreciation is extended to more than 50 local government engineers, planners, technicians and biologists from across the Province, who reviewed and commented on the 2nd draftof this document.

GGeeoorrggiiaa BBaassiinn EEccoossyysstteemm IInniittiiaattiivveeWWoorrkkiinngg TTooggeetthheerr ffoorr tthhee GGeeoorrggiiaa BBaassiinn

Ministries of Community, Aboriginal andWomen’s Services and Water, Land and AirProtection

The Guidebook draws heavily on case study experience from various local governments and developers in BC. We wish to thank the following local governments for allowing usto use their material and benefit from their experience.

Questions or Comments? Please contact:

Peter Law Laura MacleanEcosystem Biologist Non-Point Source Pollution Prevention CoordinatorBritish Columbia Ministry of Water, Land and Air Protection Environment CanadaPh.: (250) 751-3229 Ph.: (604) 666-2399Fax: (250) 751-3103 Fax: (604) 666-7294Email: [email protected] Email: [email protected]

City of Chilliwack

Greater VancouverRegional District

City of Coquitlam

District of Maple Ridge

STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIA

MAY 2002

How to Use the Guidebook The Stormwater Planning Guidebook is structured to meet the information needs of different audiences: from senior managers and elected officials… to those professional planning and engineering staff who are tasked with implementing early action… to land developers and the consulting community.

The Guidebook is Structured in Three Parts: q Part A – The Problem and Principles: written for senior managers, elected

officials and those wanting a general introduction to integrated stormwater management.

q Part B – The Solutions: written mainly for engineers and planners, this part provides examples of how to achieve integrated stormwater management at both planning and site levels.

q Part C – The Process: written for administrators and the complete range of stakeholders who will be involved in making the move from planning to action, this part defines roles, methods, means and timing for integrated stormwater management.

For readers who are new to integrated stormwater management, Part A is required reading.

Readers looking for a sense of what integrated stormwater management means on the ground will enjoy the examples in Part B.

Those wanting to start or fund an integrated stormwater management plan or program will find organizational advice in Part C.

The Guidebook draws heavily on case study experience by leading local governments and developers in BC. The illustrations are adapted from projects by the authors.

The overall objective of this Guidebook is to offer a common sense, effective and affordable approach to integrated stormwater management.

Table of Contents

Stormwater Planning Guidebook

STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIA TABLE OF CONTENTS

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Table of Contents

EXECUTIVE SUMMARY Stormwater Component of Liquid Waste Management Plans ................................... ES-1

Part A – Why Integrated Stormwater Management?................................................ ES-2

Part B – Integrated Stormwater Management Solutions ........................................... ES-2

Part C – Moving from Planning to Action ................................................................ ES-2

ADAPT – The Guiding Principles of Integrated Stormwater Management ................. ES-3

CURE – The Elements of an Action Plan ................................................................ ES-6

Translating a Vision into Action .............................................................................. ES-6 PART A – WHY INTEGRATED STORMWATER MANAGEMENT? CHAPTER 1 LAND USE CHANGE DRIVES STORMWATER MANAGEMENT 1.1 Impacts Flow Down the Watershed ........................................ 1-1

1.2 Potential Stormwater Impacts will Accelerate Due to Population Growth Pressure and Climate Change ................... 1-7

1.3 Integrating Stormwater Solutions with Land Use Change ......... 1-8 1.4 Local Government Responsibility for Drainage ........................ 1-9 1.5 History and Evolution of Stormwater Management................... 1-11 CHAPTER 2 THE SCIENCE BEHIND INTEGRATED STORMWATER MANAGEMENT 2.1 Developing a Common Understanding.................................... 2-1 2.2 The Natural versus Urban Water Balance ............................... 2-3 2.3 Understanding Changes in Hydrology ..................................... 2-6 2.4 Factors that Limit the Health of Aquatic Resources .................. 2-9 2.5 Managing Complexity ............................................................ 2-11

PART B – INTEGRATED STORMWATER MANAGEMENT SOLUTIONS CHAPTER 3 THE SCOPE OF INTEGRATED STORMWATER MANAGEMENT 3.1 Overview and Context ........................................................... 3-1 3.2 The Transition from Traditional to Integrated Stormwater Management ......................................................................... 3-3

3.3 Plan at Four Scales – Regional, Watershed, Neighbourhood and Site................................................................................ 3-5

3.4 Integrated Stormwater Management Planning ......................... 3-6 3.5 The Relationship Between Stormwater and Land Use.............. 3-7 3.6 A Guide to Part B .................................................................. 3-9 CHAPTER 4 POLICIES FOR INTEGRATION OF LAND USE PLANNING AND STORMWATER MANAGEMENT

4.1 Policy Tools for Implementing Integrated Stormwater Management Solutions .......................................................... 4-1

4.2 Liquid Waste Management Plans ........................................... 4-3 4.3 Relationship Between OCPs and LWMPs ............................... 4-5 4.4 Stormwater Management Goals, Objectives and Policies ......... 4-6 4.5 Policy Transition in a Rural Regional District ........................... 4-13 CHAPTER 5 SETTING PRIORITIES FOR EARLY ACTION 5.1 Knowledge-Based Approach.................................................. 5-1 5.2 At-Risk Methodology ............................................................. 5-1 5.3 Case Study: Stormwater Priorities in the Regional District of Nanaimo ........................................................................... 5-5 5.4 The Role of Mapping ............................................................. 5-8


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CHAPTER 6 SETTING PERFORMANCE TARGETS AND DESIGN GUIDELINES 6.1 The Role of Performance Targets........................................... 6-1 6.2 Defining the Target Condition................................................. 6-3 6.3 Moving from Science to Site Design ....................................... 6-7 6.4 Managing the Complete Spectrum of Rainfall Events............... 6-9 6.5 Methodology for Setting Performance Targets and Site Design Guidelines .......................................................... 6-13 CHAPTER 7 SITE DESIGN SOLUTIONS FOR ACHIEVING PERFORMANCE TARGETS

7.1 Overview of Site Design Strategies for Achieving Performance Targets............................................................. 7-1 7.2 Low Impact Development Practices ........................................ 7-2 7.3 Stormwater Source Control Practices ..................................... 7-5 7.4 Type 1 Source Control - Absorbent Landscaping ..................... 7-9 7.5 Type 2 Source Control - Infiltration Facilities ........................... 7-14 7.6 Type 3 Source Control - Green Roofs ..................................... 7-31 7.7 Type 4 Source Control - Rainwater Re-use ............................. 7-36 7.8 Applying Source Controls to Mitigate Extreme Cloudbursts ...... 7-41 7.9 Communicating Performance Targets to Developers ............... 7-42 CHAPTER 8 WATERSHED CONTEXT FOR SITE DESIGN SOLUTIONS 8.1 Determining What is Achievable at the Watershed Scale ......... 8-1 8.2 Watershed Retrofit Case Studies............................................ 8-3 8.3 Achieving Watershed Protection or Restoration ....................... 8-9

PART C – MOVING FROM PLANNING TO ACTION CHAPTER 9 DEVELOPING AND IMPLEMENTING AN INTEGRATED STORMWATER

MANAGEMENT PLANS (ISMP) 9.1 Overview of ISMPs................................................................ 9-1 9.2 Process for Developing and Implementing an ISMP ................ 9-5

9.3 Step #1: Secure Political Interest and Support ......................... 9-7 9.4 Step #2: Frame the Watershed Problems and Opportunities .... 9-9

9.5 Step #3: Develop Objectives and Alternative Scenarios ........... 9-10 9.6 Step #4: Collect Meaningful Data and Refine Scenarios ........... 9-18

9.7 Step #5: Evaluate Alternatives and Develop Component Plans .................................................................. 9-20

9.8 Step #6: Develop an Implementation Program ........................ 9-22 9.9 Step #7: Refine Through Adaptive Management ...................... 9-23 9.10 Synopsis of the Seven-Step Process for ISMP Development

and Implementation ............................................................... 9-25 CHAPTER 10 FUNDING AN INTEGRATED STORMWATER MANAGEMENT PLAN

(ISMP) 10.1 Framing the Question ............................................................ 10-1 10.2 Making Choices .................................................................... 10-2 10.3 Who Pays?........................................................................... 10-3 10.4 Sources of Funding ............................................................... 10-5

10.5 Setting Up a Stormwater Utility............................................... 10-6 10.6 Regional Approach................................................................ 10-8 CHAPTER 11 BUILDING CONSENS US AND IMPLEMENTING CHANGE 11.1 Developing a Shared Vision ................................................... 11-1 11.2 Overcoming Barriers to Implementation .................................. 11-3 11.3 Moving from Planning to Action ............................................. 11-5 11.4 Translating a Shared Vision into Action................................... 11-6 11.5 Using Working Sessions to Build Consensus .......................... 11-9 11.6 Administering an Action Plan.................................................. 11-11 11.7 Defining Roles and Aligning Responsibilities ........................... 11-15 11.8 Creating Change through Public Communication..................... 11-17 BIBLIOGRAPHY


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LIST OF FIGURES Figure 1-1 Components of the Natural Water Balance..................................... 1-1 Figure 1-2 Natural Rainforest......................................................................... 1-2 Figure 1-3 Single Family Development ........................................................... 1-2 Figure 1-4 Commercial Development ............................................................. 1-2 Figure 1-5 Multiple Drainage Culvert Installations ............................................ 1-3 Figure 1-6 Channel Down-Cutting (due to increased volume)........................... 1-3 Figure 1-7 Habitat Destruction (due to bedload deposition).............................. 1-3 Figure 1-8 Impact of Increasing Urbanization on Stream Corridor Ecology ........ 1-5 Figure 1-9 Flooding in Urbanizing Environment ............................................... 1-7 Figure 1-10 The Stormwater Dilemma .............................................................. 1-8 Figure 2-1 Example Annual Water Balance..................................................... 2-4 Figure 2-2 Example Distribution of Annual Rainfall .......................................... 2-5 Figure 2-3 Changes in Hydrology ................................................................... 2-6 Figure 2-4 Impact of Changes in Hydrology on Watercourse Erosion and......... 2-7 Base Flow Relationships Figure 2-5 Reference Levels for Land Use Planning........................................ 2-9 Figure 2-6 Change to an Integrated Approach ................................................ 2-11 Figure 3-1 Rainfall Flow in Watercourses ....................................................... 3-1 Figure 3-2 Elements of Transition .................................................................. 3-3 Figure 3-3 A Truly Integrated Plan of Action.................................................... 3-6 Figure 4-1 Complementary and Iterative Tools................................................ 4-2 Figure 5-1 Knowledge-Based Approach ......................................................... 5-2 Figure 6-1 The Adaptive Management Approach ............................................ 6-2 Figure 6-2 Science-Based Strategy for Managing the Complete Spectrum ....... 6-7 of Rainfall Events Figure 6-3 Typical Frequency Distribution of Annual Rainfall............................ 6-10 Figure 6-4 Typical Volume Distribution of Annual Rainfall ................................ 6-10 Figure 6-5 Six-step Process for Setting Performance Targets and Site Design Criteria ....................................................................... 6-13 Figure 6-6 Chilliwack Rainfall Analysis ........................................................... 6-16 Figure 6-7 Distribution of Annual Rainfall Volume (Sardis) ............................... 6-18

Figure 6-8 City of Chilliwack – Infiltration Area Required to Achieve Rainfall Capture Target ...............................................................................6-21 Figure 6-9 Performance Monitoring Requirements ............................................6-29 Figure 7-1 Creation of Landscape Soil..............................................................7-9 Figure 7-2 Effect of Soil Depth on Performance of Absorbent Landscaping ........7-10 Figure 7-3 Effect of Rainfall on Benefits of Absorbent Landscaping ....................7-11 Figure 7-4 Benefits of Absorbent Landscaping (Runoff Volume Reduction).........7-12 Figure 7-5 Benefits of Absorbent Landscaping (Peak Runoff Rate Reduction) ....7-12 Figure 7-6a&b Benefits of Impervious Surface Disconnection ..................................7-14 Figure 7-7a&b Infiltration Chamber.........................................................................7-15 Figure 7-8a&b Bioretention Facilities ......................................................................7-16 Figure 7-9 Infiltration Trench............................................................................7-16 Figure 7-10 Infiltration Swale Along Roadway .....................................................7-16 Figure 7-11 Effect of Rainfall on Infiltration Facility Performance ..........................7-18 Figure 7-12 Effect of Depth and Facility Type on Infiltration Performance .............7-19 Figure 7-13a&b Infiltration Facility Performance .......................................................7-20 Figure 7-14 Affordability Thresholds for Infiltration Facilities ................................7-21 Figure 7-15a&b Infiltration Facility Performance .......................................................7-22 Figure 7-16a&b Infiltration Facility Performance .......................................................7-23 Figure 7-17 Achievable Level of Runoff Volume Reduction ..................................7-24 Figure 7-18 Pervious Pavers .............................................................................7-25 Figure 7-19 Volume Reduction Benefits of Pervious Paving.................................7-25 Figure 7-20 Pervious Decks ..............................................................................7-26 Figure 7-21 Stormwater Management - Incorporating New Strategies ..................7-27 Figure 7-22 Designing Parking Lots that Infiltrate ................................................7-28 Figure 7-23 Lightweight Extensive Green Roof ...................................................7-31 Figure 7-24 Absorbent Soils and Flow Control Over Parking Garage....................7-31 Figure 7-25 Effect of Rainfall on Green Roof Performance...................................7-32 Figure 7-26a&b Effect of Soil Depth on Green Roof Performance ..............................7-33 Figure 7-27a&b Benefits of Green Roofs for Different Land Uses ...............................7-34 Figure 7-28a&b Rainwater Re-use...........................................................................7-36 Figure 7-29a&b Benefits of Rainwater Re-use ..........................................................7-37 Figure 7-30 Impact of Surface Parking on Effectiveness of Rainwater Re-use.......7-38


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Figure 7-31 Effect of Rainfall on the Benefits of Rainwater Re-use.................. 7-38 Figure 7-32 Effect of Storage Volume on Benefits of Rainwater Re-use........... 7-39 Figure 7-33 Effectiveness of Source Controls at Reducing Peak Runoff from an Intense Cloudburst ................................................................ 7-41 Figure 8-1 GVRD Case Study Watersheds .................................................. 8-3 Figure 8-2 Re-development Impacts in McKinney Creek Watershed.............. 8-5 Figure 8-3a-b-c McKinney Creek Watershed Retrofit Scenarios ............................ 8-6 Figure 8-4 Projected Densification in Quibble Creek Watershed.................... 8-7 Figure 8-5a-b-c Quibble Creek Watershed Retrofit Scenarios ............................... 8-8 Figure 9-1 Planning Framework .................................................................. 9-1 Figure 9-2 ISMP Building Blocks................................................................. 9-3 Figure 9-3 Seven Steps for Developing and Implementing an ISMP .............. 9-6 Figure 9-4 Alternative Visions for the Long-Term Environmental Health of Stream Corridors.................................................................... 9-11 Figure 9-5 Modeling Hierarchy .................................................................... 9-15 Figure 9-6 ISMP Components..................................................................... 9-20 Figure 9-7 Adaptive Framework .................................................................. 9-23 Figure 11-1 Shared 50-Year Vision for Watershed Restoration ....................... 11-2 Figure 11-2 Organizational versus Analytical Issues ....................................... 11-4 Figure 11-3 Building Consensus ................................................................... 11-9

LIST OF TABLES Table 1-1 Origin and Evolution of Integrated Stormwater Management..............1-13 in British Columbia Table 3-1 Presumed Relationship bet ween Imperviousness and Land Use........3-7 Table 3-2 Ten Principles that Define the Relationship Between Stormwater Management and Land Use ..........................................3-8 Table 4-1 Land Use Changes with the Potential to Affect Stormwater Quantity and Quality .......................................................................4-13 Table 4-2 Regional District of Nanaimo Stormwater Action Plan........................4-17 Table 5-1 Structure for Focused Working Sessions ..........................................5-4 Table 6-1 Rainfall Spectrum for Various Location in BC....................................6-9 Table 9-1 ISMP Components (from GVRD Template) ......................................9-4 Table 9-2 Decision Criteria to Select Strategies for Stream Management ..........9-13 Table 9-3 Synopsis of the Seven-Step Process for ISMP Development and Implementation ........................................................................9-26 Table 10-1 Who Pays for Stormwater Management Infrastructure? .....................10-3 Table 10-2 Who Operates and Maintains Stormwater Management Infrastructure? ...........................................................10-4 Table 11-1 Adaptive and Collaborative Process for Translating a Shared Vision into Action ................................................................11-8 Table 11-2 Finance and Administration Protocol for Implementing an Action Plan ....................................................................................11-11 Table 11-3 Implementation Actions for the Como Creek ISMP ...........................11-13 Table 11-4 Creating Change Through Public Communication ............................11-17 Table 11-5 Ingredients to Build Consensus .......................................................11-18

Table of Contents q Stormwater Component of Liquid Waste Management Plans

♦ An OCP Provides the Foundation for a LWMP ♦ Integrated Stormwater Management Planning

q Part A – Why Integrated Stormwater Management? q Part B – Integrated Stormwater Management Solutions

♦ Step #1 – Identify At-Risk Drainage Catchments ♦ Step #2 – Set Preliminary Performance Targets ♦ Step #3 – Select Appropriate Stormwater Management Site Design Solutions

q Part C – Moving from Planning to Action q ADAPT- The Guiding Principles of Integrated Stormwater Management

♦ Guiding Principle 1 - Agree that Stormwater is a Resource ♦ Guiding Principle 2 - Design for Complete Spectrum of Rainfall Events ♦ Guiding Principle 3 - Act on a Priority Basis in At-Risk Catchments ♦ Guiding Principle 4 - Plan at Four Scales – Regional, Watershed, Neighbourhood and Site ♦ Guiding Principle 5 - Test Solutions and Reduce Costs by Adaptive Management

q CURE – The Elements of an Action Plan q Translating a Vision into Action

♦ Building Blocks

Executive Summary


STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIA EXECUTIVE SUMMARY

MAY 2002


MAY 2002

ES-1

Stormwater management in British Columbia is a key component of protecting quality of life, property and aquatic ecosystems. The science and practice of stormwater management is constantly evolving, in British Columbia and around the world. Within BC, the range of stormwater management activity varies from completely unplanned in many rural areas, to state-of-the-art in some metropolitan centres. The purpose of this Guidebook is to provide a framework for effective stormwater management that is usable in all areas of the province. The Guidebook presents a methodology for moving from planning to action that focuses the limited financial and staff resources of governments, non-government organizations and the development community on implementing early action where it is most needed. The Guidebook is organized in three parts: Part A defines the problem, Part B provides solutions and Part C defines the process.

The Guidebook provides a comprehensive understanding of the issues and a framework for implementing an integrated approach to stormwater management. Case study experience underpins the approaches and strategies that are presented in the Guidebook.

Stormwater Component of Liquid Waste Management Plans In British Columbia, the Local Government Act has vested the responsibility for drainage with municipalities. With the statutory authority for drainage, local governments can be held liable for downstream impacts that result from changes to upstream drainage patterns – both volume and rate. The Act also enables local governments to be proactive in implementing stormwater management solutions that are more comprehensive than past practice.

Furthermore, a stormwater component is a requirement for approved Liquid Waste Management Plans (LWMPs). Guidelines for developing a LWMP were first published in 1992. LWMPs are created by local governments under a public process in co-operation with the Province.

An OCP Provides the Foundation for a LWMP There is a clear link between the land use planning required of local governments in the Local Government Act and the LWMP process. In most cases where an Official Community Plan (OCP) is in place, the local government planning statement (bylaw) will form the basis for a LWMP. The purposes of a LWMP are to minimize the adverse environmental impact of the OCP and ensure that development is consistent with Provincial objectives.

OCPs tend to be led by planners, with input from engineers on infrastructure sections. LWMPs tend to be led by engineers, with little or no input from planners. Both processes involve approval by a Local Council or a Regional Board.

In some cases, a LWMP process may be a trigger that focuses attention on stormwater management. Public concern related to flooding or habitat loss may be the trigger. Or an OCP public process may communicate public interest in raising local environmental and habitat protection standards.

Whatever the driver, at the end of the process an OCP should include goals and objectives for stormwater management. These goals and objectives, or a variant of them, might first reside in a LWMP, and then be adapted to the OCP in the next review process. Or they may originate in the OCP process, and then be detailed through a LWMP. Either way is entirely acceptable.

Integrated Stormwater Management Planning In British Columbia, the term Integrated Stormwater Management Plan (ISMP) has gained widespread acceptance by local governments and the environmental agencies to describe a comprehensive approach to stormwater planning. The purpose of an ISMP is to provide a clear picture of how to be proactive in applying land use planning tools to protect property and aquatic habitat, while at the same time accommodating land development and population growth.

Executive Summary


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Part A – Why Integrated Stormwater Management? Part A identifies problems associated with traditional stormwater management and provides the rationale for a change from traditional to integrated stormwater management. Some guiding principles of integrated stormwater management are introduced. Part A also builds a science-based understanding of how natural watersheds function and how this function is affected by land use change.

Part B – Integrated Stormwater Management Solutions Part B outlines the scope and policy framework for integrated stormwater management, and presents a cost-effective methodology for developing stormwater solutions.

Step #1 - Identify At-Risk Drainage Catchments A methodology is presented for identifying at-risk drainage catchments to focus priority action. The methodology relies on a roundtable process that brings together people with knowledge about future land use change, high-value ecological resources and chronic flooding problems. The key is effective integration of planning, engineering and ecological perspectives.

Step #2 - Set Preliminary Performance Targets A methodology is presented for:

q Developing watershed performance targets based on site-specific rainfall data, supplemented by streamflow data (if available) and on-site soils investigations

q Translating these performance targets into design guidelines that can be applied at the site level to mitigate the impacts of land development

The Guidebook documents British Columbia case studies of stormwater policies and science-based performance targets applied to both greenfield and urban retrofit scenarios.

Step #3 - Select Appropriate Stormwater Management Site Design Solutions Guidance is provided for selecting appropriate site design solutions to meet performance targets. Examples include:

q Design and performance of stormwater source controls for various land uses

q Watershed scale modeling of the effectiveness of site design solutions British Columbia case studies are examined for greenfield and urban retrofit scenarios. A ‘Water Balance Model’ is also applied for linking performance targets to design guidelines for source control and runoff conveyance.

Part C – Moving from Planning to Action Part C describes a process that will lead to better stormwater management solutions.

The role and design of action plans are introduced to bring a clear focus to what needs to be done, with what priority, by whom, with related budgets.

Tips are provided on processes that produce timely and high-quality decisions.

Part C also provides guidance for organizing an administrative system and financing strategy for stormwater management.

A final section on building consensus and implementing change describes how to develop a shared vision and overcome barriers to change. Two acronyms provide a useful summary of the principles and elements of integrated stormwater management:

A D A P T to the

C U R E


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ADAPT –

The Guiding Principles of Integrated Stormwater Management

The acronym ADAPT summarizes five guiding principles for integrated stormwater management. The Guidebook is based upon these five principles.

gree that stormwater is a resource esign for the complete spectrum of rainfall events

ct on a priority basis in at-risk drainage catchments

lan at four scales – regional, watershed, neighbourhood & site

est solutions and reduce costs by adaptive management.


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Guiding Principle 1 - Agree that Stormwater is a Resource Stormwater is no longer seen as just a drainage or flood management issue but also a resource for:

q fish and other aquatic species q groundwater recharge (for both stream summer flow and for potable

water) q water supply (e.g. for livestock or irrigation) q aesthetic and recreational uses

Guiding Principle 2 - Design for the Complete Spectrum of Rainfall Events

Integrated stormwater solutions require site design practices that provide:

q Rainfall Capture for Small Storms (runoff volume reduction and water quality control) – Capture the small frequently occurring rainfall events at the source (building lots and streets) for infiltration and/or re-use.

q Runoff Control for Large Storms (runoff rate reduction) – Store the runoff from the infrequent large storms (e.g. a mean annual rainfall), and release it a rate that approximates the natural forested condition.

q Flood Risk Management for the Extreme Storms (peak flow conveyance) – Ensure that the drainage system can safely convey extreme storms (e.g. a 100-year rainfall).

The Integrated Strategy Guiding Principle 2 forms the foundation of integrated stormwater solutions that mimic the most effective stormwater management system of all - a naturally vegetated watershed. This means that rainfall from frequent small events must be infiltrated into the ground or re-used within the watershed, as illustrated below.

20%Large Storms

75%Small Storms

5%Extreme Storms

Total Rainfall Volume

Infil

trat

ion

StormwaterManagementStrategy forImpervious

Areas

TypicalRainfallVolume

Distribution

HydrologicPathway

Rainfall Capture Runoff Control

DeepGroundwater

Evaporation-Transpiration

Infiltrate or Reuse Small Storms at the Source to Reduce

Total Runoff Volume

Reuse

Runoff

Integrated Strategy for Managing theComplete Spectrum of Rainfall Events

Provide Storage to Control the Rate of Runoff from Large Storms

StorageRelease

Flood RiskManagement

Ensure that the Stormwater Systemcan Safely Convey

Extreme Storms

ControlledFlow


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Comparison with Conventional Stormwater Management Conventional ‘flows-and-pipes’ stormwater management is limited because it focuses only on the fast conveyance of the extreme storms and often creates substantial erosion and downstream flooding in receiving streams.

Similarly, a detention-based approach is only a partial solution because it allows the small storms that comprise the bulk of total rainfall volume to continue to create erosion and impacts on downstream aquatic ecosystems.

Neither of these approaches fully prevents the degradation of aquatic resources or flooding risks to property and public safety.

In contrast, the Guidebook approach is to eliminates the root cause of ecological and property impacts by designing for the complete spectrum of rainfall events. Solutions described in the Guidebook include conventional, detention, infiltration and re-use approaches for rainfall capture, runoff control and flood risk management.

Guiding Principle 3 - Act on a Priority Basis in At-Risk Drainage Catchments

Priority action should be focused in at-risk drainage basins where there is both high pressure for land use change and a driver for action. The latter can be either:

q a high-value ecological resource that is threatened, or q an unacceptable drainage problem The stormwater management policies and techniques implemented in at-risk catchments become demonstration projects.

Guiding Principle 4 - Plan at Four Scales – Regional, Watershed, Neighbourhood and Site

Integrated stormwater management must be addressed through long-term planning at each of the regional, watershed, neighbourhood and site scales. q At the Regional and Watershed Levels – Establish stormwater

management objectives and priorities q At the Neighbourhood Level – Integrate stormwater management

objectives into community and neighbourhood planning processes q At the Site Level – Implement site design practices that reduce the

volume and rate of surface runoff and improve water quality Guiding Principle 5 - Test Solutions and Reduce Costs by Adaptive Management

Performance targets and stormwater management practices should be optimized over time based on: q monitoring the performance of demonstration projects q strategic data collection and modeling As success in meeting performance targets is evaluated, the stormwater management program can be adjusted as required.


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CURE – The Elements of an Action Plan The acronym CURE focuses attention on the four key types of actions that must all work together to implement integrated stormwater management solutions: q CAPITAL INVESTMENT – Short-term capital investment will be needed to

implement early action in at-risk drainage basins. Improvements to existing drainage system are often the most significant capital investments required. A financing plan should provide an ongoing source of funds for watershed improvements.

q UNDERSTANDING SCIENCE – Improved understanding of a watershed, the

nature of its problems, and the effectiveness of technical solutions is key to an adaptive approach. Stormwater management practices can be optimized over time through the monitoring of demonstration projects, combined with selective data collection and modeling.

q REGULATORY CHANGE – Changes in land use and development regulations are needed to achieve stormwater performance targets. Changes to land use planning and site design practices are needed to eliminate the root cause of stormwater related problems. These changes must be driven by regulation.

q EDUCATION AND CONSULTATION – Changes to land use planning and site

design practices can only be implemented by building support among city staff, the general public and the development community through education and consultation.

Translating a Vision into Action It is important to establish a long-term shared vision at the start of any watershed planning initiative. A vision that is shared by all stakeholders provides direction for a long-term process of change. The vision becomes a destination, and an action plan provides a map for getting there.

Actions plans must be long-term, corresponding to the time frame of the vision. Action plans must also evolve over time.

Ongoing monitoring and assessment of progress towards a long-term vision will improve understanding of the policy, science and site design components of integrated stormwater management. This improved understanding will:

q Lead to the evolution of better land development and stormwater management practices

q Enable action plans to be adjusted accordingly

An adaptive management approach to changing stormwater management practices is founded on learning from experience and adjusting for constant improvement.

Building Blocks The Guidebook elaborates on three fundamental objectives that become building blocks for a long-term process of change:

q Achievable and Affordable Goals - Apply a science-based approach to create a shared vision for improving the health of individual watersheds over time.

q Participatory Decision Process - Build stakeholder consensus and support for implementing change, and agree on expectations and performance targets.

q Political Commitment – Take action to integrate stormwater management with land use planning.

Chapter One 1.1 Impacts Flow Down the Watershed

q Stormwater q Changes to the Natural Water Balance q Property Impacts q Ecological Impacts on Species at Risk q Water Quality Impacts q Financial Impacts q Lessons Learned

1.2 Potential Stormwater Impacts will Accelerate Due to Population Growth Pressure and Climate Change q Population Growth Pressure q Climate Change

1.3 Integrating Stormwater Solutions with Land use Change

q Recent Approaches Have Only Provided Partial Solutions q Preventing History from Repeating Itself

1.4 Local Government Responsibility for Drainage

q Liability for Downstream Impacts Due to Changes in the Water Balance q Authority to Implement Integrated Solutions

1.5 History and Evolution of Stormwater Management

q North American Context q British Columbia Context


Land Use Change Drives Stormwater Management

STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIA PART A – WHY I NTEGRATED STORMWATER MANAGEMENT?

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1.1 Impacts Flow Down the Watershed Figure 1-1 illustrates schematically how water is recycled in nature. Water evaporates from lakes, rivers and oceans. It then becomes water vapour and forms clouds. It falls to the earth as precipitation, then it evaporates again. This ‘hydrological cycle’ never stops. Water keeps moving and changing phases from solid to liquid to gas, over and over again. In this Guidebook, this process is described as the natural ‘Water Balance’.

Figure 1-1 Components of the Natural Water Balance

Stormwater Stormwater is the component of runoff that is generated by human activities. Stormwater is created when land development alters the natural Water Balance. When vegetation and soils are replaced with roads and buildings, less rainfall infiltrates into the ground, less gets taken up by vegetation and more becomes surface runoff.

The biggest increments of change - to the Water Balance in general, and to the surface runoff component in particular - occur when forested land is first cleared, then ditched, and finally paved or roofed over.

Until recently, the traditional approach to drainage has been to remove runoff as quickly as possible from developed areas. As a result, traditional urban design is very efficient in collecting, concentrating, conveying and discharging stormwater to receiving waters.

In British Columbia, stormwater management has traditionally been a function of local government or highway engineers, who have developed an expertise in conveying stormwater efficiently. Increasingly, stormwater management is becoming a shared responsibility with land use planners.

Guidebook Context To mitigate the cumulative impacts of stormwater resulting from changes to the natural Water Balance, the British Columbia Ministry of Water, Land and Air Protection has developed this Guidebook to assist local governments, engineers and planners in clearly understanding the broader issues and the strategies currently available to correct stormwater-related problems.

A stormwater management component is a requirement for approved Liquid Waste Management Plans (LWMPs). The Ministry will encourage any progressive steps a local government may want to take to incorporate stormwater planning into their existing LWMP.

A core concept is that stormwater is a resource to be protected. Achieving this goal requires full integration of stormwater management with land use planning.


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Changes to the Natural Water Balance

Runoff volume increases in proportion to impervious area (hard, non-absorbent surfaces). Land uses with extensive roof and paving areas create more runoff than land uses with extensive areas of absorbent soils and forest cover. Figure 1-2 illustrates the Water Balance for a natural forest. The examples on Figures 1-3 and 1-4 then illustrate what happens to the Water Balance when the forest is developed for residential and/or commercial uses, respectively.

Figure 1-2 Natural Rainforest

Traditional ditch and pipe systems have been designed to remove runoff from impervious surfaces as quickly as possible and deliver it to receiving waters. The resulting stormwater arrives at the receiving waters much faster and in greater volume than under natural conditions. Changes in the natural Water Balance result in four categories of impacts: property, ecological, water quality and financial/political. An overview of each category is provided in the pages that follow. Failure to manage stormwater resulting from land use change can cause flooding, loss of aquatic habitat and water pollution in downstream receiving waters.

Residential30%-50% impermeable

35% evapotranspiration

30% runoff

35% infiltration

75% runoff

5% infiltration Commercial70%-100% impermeable


Figure 1-4 Commercial Development


50% infiltration

10% runoff


Natural Rainforest0% impermeable

Figure 1-3 Single Family Development


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Property Impacts The width and depth of a stream are determined by the volume and rate of water that it conveys. Therefore, increases in flow volume and peak flow rates resulting from land development cause erosion on the sides and bottom of the channel. Figure 1-5 shows how additional culverts have been installed at a road crossing in order to handle the increased volume after upstream land clearing and ditching has occurred.

The material from these eroding banks (as shown on Figure 1-6) moves downstream as ‘bedload’, and settles out on the more gentle grades in the stream (Figure 1-7). These gentle grades are often located in the floodplain. These changes in stormwater flows and stream morphology often create both loss of property where erosion takes place, and increased flooding in the floodplain as it is filled in by sediments. This often results in damage to private property and agricultural land, and can pose a potential threat to public safety. The most common property impact resulting from the increase in runoff is the accumulation of nuisance water on private property and public spaces downstream of development areas.

Figure 1-5 Multiple Drainage Culvert Installations

Figure 1-6 Channel Down-Cutting (due to increased volume)

Figure 1-7 Habitat Destruction (due to bedload deposition)


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Ecological Impacts on Species at Risk Figure 1-8 illustrates how:

q The cumulative effects of increasing impervious area in a watershed combined with loss of riparian corridor integrity (as shown in the first two rows), alter the natural Water Balance and impact stream corridor ecology (as shown in the last two rows).

q The resulting increase in runoff volume causes watercourse erosion and progressive degradation of the channel cross-section (refer to middle row).

q The consequence of these cumulative changes is a progressive decline in stream corridor biodiversity and abundance for cold-water fish and clear water indicators, and a progressive transition to warm-water species and pollutant indicators (as shown in the last two rows).

Eroded material (Figure 1-6) creates turbidity, or dirty water, that can irritate fish gills and make it difficult for fish to find their food. Eroded sediments can cover spawning beds, smothering fish eggs and young that reside in the gravel and possibly blocking access to spawning areas for the next generation (Figure 1-7).

The decrease in infiltration (due to replacement of soil and vegetation with hard surfaces) can also have impacts on fish because it reduces the slow, constant groundwater supply that keeps streams flowing in dry weather. This can lead to water levels that are inadequate to provide fish with access to their spawning areas, and can even cause streams to dry up in the summer.

Driving Force for New Approaches Stemming and reversing the decline of wild salmon populations has led to questioning of the most basic assumptions that used to guide – and in many communities still guide – how we plan and manage development. This questioning has resulted in new approaches to land development and stormwater management. These new approaches are being advanced and implemented throughout the Pacific Northwest, and especially in the Georgia Basin.

The decline of wild fish populations is not limited to the Georgia Basin. In Okanagan Lake, for example, degradation of tributary streams and loss of aquatic habitat have similarly contributed to the decline of the kokanee fishery.


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Figure 1-8


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Water Quality Impacts Although of BC’s water quality is generally good, people are increasingly aware that the province is experiencing localized water pollution problems. Every year there are reports of public beach closures, contaminated sediments, algal blooms, aquatic weed infestations, fish kills, shellfish harvesting closures, boil-water advisories, outbreaks of waterborne diseases, and contaminated groundwater. BC’s efforts to protect water quality by regulating ‘end-of-pipe’ point discharges from municipal and industrial outfalls have generally been successful.

It is now recognized that the major remaining cause of water pollution is from non-point sources (NPS), including stormwater runoff. Stormwater contains contaminants such as hydrocarbons and heavy metals derived from vehicle exhaust, brakes and leaked fluids, as well as nutrients, pesticides and bacteria from urban and agricultural land uses. When stormwater flows over large paved surfaces on warm days, it can increase to temperatures that are unsuitable for cold-water fish like salmon and trout. The result can be immediate fish kills in receiving streams, or chronic, long-term impairment of fish and other aquatic species.

Financial Impacts Local governments and developers are finding that drainage costs are becoming a major portion of their capital outlay. The capital cost of land development with traditional piped solutions can be a significant detriment to affordable housing. In recent years, this has been one of the drivers for change. Reducing costs is providing an incentive for innovation. An example of this change in thinking is presented below:

Although the Greater Vancouver region is spending about $33 million annually on stormwater management, “….in many areas of the region, current approaches to stormwater management and land development do not adequately protect the environment of small streams in watersheds experiencing significant population growth.”

Source: page 1 of Executive Summary Stage 2 Liquid Waste Management Plan, 1999 Greater Vancouver Regional District

Finding a Better Way Installation of drainage pipes without mitigating measures often creates erosion problems and/or flooding downstream in receiving watercourses. These risks can create threats to property and public safety, resulting in exposure to litigation.

To avoid further impacts and litigation, local governments are now beginning to address the cumulative erosion and flooding impacts resulting from development. This creates a further cost burden for additional drainage infrastructure, and for increased staff time devoted to maintenance of at-risk culverts and degraded floodplains.

In many cases, solving downstream problems by piping or armouring creeks is no longer environmentally acceptable, either to senior agencies or to the public.

This set of problems creates both financial and political imperatives to find a better way to develop land.

Lessons Learned The essence of the foregoing discussion is captured below. These two ‘lessons learned’ provide a framework for developing land differently:

q Universal Drivers for Change - The risks and the impacts associated with stormwater have become drivers for change in the way stormwater is managed in British Columbia and in other jurisdictions around the world (e.g. the United States, Australia and New Zealand). It has been recognised that dealing with flooding and aquatic habitat issues must be integrated with decisions on land use change.

q Complementary Objectives – Integrated approaches to stormwater management acknowledge that protection of property, protection of aquatic resources, and protection of water quality are complementary objectives. Integrated approaches address each of these objectives.


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1.2 Potential Stormwater Impacts will Accelerate Due to Population Growth Pressure and Climate Change

In the future, there will be more runoff volume to manage due to the combination of:

q Population Growth – resulting in more land development plus re-development / densification of existing urbanized areas

q Climate / Weather Change – resulting in both increased seasonal rainfall and more frequent ‘cloudbursts’

Population Growth Pressure Only about 5% of BC is suitable and/or available for human development. The majority of the land area – about 90% - is owned by the Crown and is mostly mountainous terrain. The balance (5%) is protected within the Agricultural Land Reserve. The limited supply of developable (and available) land is a driving force for change. The majority of the developable land in BC is located in the southwestern portion of the province.

As regional populations grow, more and more people will need to be accommodated in existing development areas. This will result in some rural areas becoming increasingly suburban. Similarly, suburban municipalities that are close to the major population centres will become more urban as they densify. The rate and scale of development in the 1990s has already transformed most suburban development areas, especially in southern BC.

Population-driven changes are most noticeable in the Georgia Basin, throughout the Okanagan, and in many parts of the Kootenays. The Georgia Basin is a bio-region that includes Greater Vancouver, the lower Fraser Valley east to Hope, and the East Coast of Vancouver Island. The total population has reached 3 million, or about 75% of the provincial total of 4 million, and is projected to double within the next 50 years.

If there were no change in the way that land development addressed stormwater, this increase in population would lead to an increase in impervious area, with resulting stormwater impacts.

The pending land use change brings into focus the need for more effective strategies to reduce stormwater-related impacts on property and aquatic ecosystems.

Need for Early Action BC is ‘land short’. Population growth pressure will lead to increased impervious area and will place pressure on species at risk. For these reasons, there is a need to accelerate the rate of change so that stormwater management is integrated with land use planning sooner rather than later. Figure 1-9 illustrates the potential for flooding in the urban environment.

Figure 1-9 Flooding in the Urban Environment

Climate Change Rain gauge data for southwestern British Columbia suggest that precipitation frequency, intensity and duration are changing compared to the mid-20th century. Research by the University of British Columbia and Environment Canada implicate global climate change as the primary contributor to these observed trends.

Environment Canada models project increasing fall and winter precipitation, decreasing late spring-early summer precipitation, and more intense rainstorms (i.e. ‘cloudbursts’).


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1.3 Integrating Stormwater Solutions with Land use Change

Many existing older urban areas in BC have been developed without stormwater management, and have suffered the related property and ecological impacts. Local governments in these areas are facing extraordinary costs and difficulties to reduce the impacts.

Recent Approaches Have Only Provided Partial Solutions Emphasis in recent years has been on provision of community detention storage ponds in new developments. Although these ponds provide a partial solution, they only treat the consequences of increased impervious area, not the source.

Recent research by the University of Washington has shown that, in most cases, detention ponds mitigate flooding but do not prevent the ongoing channel erosion that creates property and fisheries impacts. Detention solutions also often do not support the sustained stream base flow that is critical to many fish populations in dry months.

In some areas of BC, especially in regional districts outside of the Greater Vancouver Regional District and the Capital Regional District, there is as yet little coordinated stormwater planning, even though urbanization and related impacts are accelerating.

Preventing Stormwater History from Repeating Itself By examining past experience, it is evident that the contemporary approach to drainage is changing, from being reactive to being proactive. Now, the focus is on preventing problems at the source, by integrating stormwater management with land use planning so that:

q Decisions about land use change are made with a full awareness of the potential consequences for stormwater management

q Conversely, stormwater management principles influence the details of land use and site planning

The Stormwater Management Dilemma Figure 1-10 illustrates the stormwater management dilemma – how can stormwater managers facilitate population growth and land development, while preserving the natural environment and preventing flooding in urban areas at the same time?

Figure 1-10 The Stormwater Dilemma


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1.4 Local Government Responsibility for Drainage

The courts see the impact of drainage on property as a ‘nuisance’, where a landowner’s use and enjoyment of his or her lands are interfered with as a result of actions or conduct on neighbouring lands. The courts have established precedents concerning the following:

q Right to drain land (allowing surface water to escape in a way provided by nature)

q Right to block drainage (surface water draining from higher land, as opposed to water in a natural stream)

q Measures of damages (damages will be awarded where liability is established) In British Columbia, the Local Government Act has vested the responsibility for drainage with municipalities. This Act also enables local governments to address stormwater management much more comprehensively than in the past. The challenge is to use this legislation to achieve comprehensive goals and objectives in appropriate and effective ways. Division 6 of the Act (Sections 540 – 549) gives local government the direct power to manage stormwater: http://www.qp.gov.bc.ca/statreg/stat/L/96323_15.htm#part15_division6

Liability for Downstream Impacts Due to Changes in the Water Balance With the statutory authority for drainage, local governments can be held liable for the nuisance caused by drainage to downstream property owners. To assist in understanding the scope of local government liability, three relatively recent cases are presented here. In all three cases, the Court of Appeal in the Province of BC has upheld the decisions. These cases underscore the responsibility of local government for stormwater volume management.

Case 1 - Indexed as: Kerlenmar Holdings v. Matsqui (District) and District of Abbotsford Judgement - June 1991 (From British Columbia Law Reports 56 B.C.L. R. (2d) p. 377 – 387.)

A creek running through the plaintiff’s farmland flooded regularly, and after 1971 the agricultural capacity of the land deteriorated as a result. The plaintiff brought an action in nuisance, attributing the flooding to increased urbanization in the two defendant municipalities, whose storm drains were releasing more and more water into the creek.

The trial judge awarded damages for loss of income and the municipality was required to purchase the plaintiff’s lands.

Case 2 - Indexed as: Medomist Farms Ltd. v. Surrey (District) Judgement – December 1991 (From British Columbia Law Reports 62 B.C.L. R. (2d) p. 168-177.) The defendant municipality held a road allowance across the plaintiff’s land, along which ran a drainage ditch. In 1979, the municipality permitted residential development on lands to the west of and above the plaintiff’s land. The development reduced the surface area available to absorb water, causing more runoff into the drainage ditch.

Although the ditch previously overflowed during winter wet weather periods, it now occasionally overflowed during the growing season as well as a result of the upstream residential development. The trial judge awarded damages for crop losses and ordered construction of a permanent pumping station.

Case 3 - Indexed as: Peace Portal Properties Ltd. v. Corporation of the District of Surrey Judgement - May 1990 (From Dominion Law Reports 70 D.L. R. (4th) p. 525-535.) The plaintiff operated a golf course in the defendant municipality. A creek bisected the course. The municipality had incorporated the creek into its’ drainage system. Because of increased urbanization there was a substantial increase in the flow in the creek, which caused erosion.

The plaintiff attempted to resolve the problem by replacing the natural channel of the creek with a concrete flume in the 1960s. This worked for a time, but with further urbanization and increased flow, new erosion occurred which also damaged the flume. The plaintiff proposed certain remedial work and sought contribution from the defendant. The defendant rejected the request.

The plaintiff completed the remedial work, in the process raising some of the greens and fairways. He then brought action against the municipality to recover the cost. The trial judge concluded that the evidence amply supported that nuisance of the increased flow caused the erosion and the municipality was held responsible.

http://www.qp.gov.bc.ca/statreg/stat/L/96323_15.htm#part15_division6


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Authority to Implement Integrated Stormwater Solutions Local governments have extensive and very specific tools available to them. They also have the discretion to use them or not. Decisions about a local government’s appropriate level of involvement in stormwater and stream corridor management must therefore be guided by a set of clear, broadly agreed-upon objectives, as well as an understanding of the need for balance with other competing objectives and interests.

Some key Local Government Act planning, regulation, development approval and servicing provisions applicable to stormwater management are summarized below:

Regional Growth Strategy and Official Community Plan Goals Section 849 (2) provides goal statements for:

q Protecting environmentally sensitive areas q Reducing and preventing air, land and water pollution q Protecting the quality and quantity of groundwater and surface water

Prohibition of Pollution Section 725.1 enables local governments to enact bylaws prohibiting water pollution and to impose penalties for contravening these.

Soil Deposit and Removal (Erosion Control) Section 723 enables local governments to include erosion control and sediment retention requirements associated with soil deposition and removal.

Zoning Section 903 enables the prohibition or siting of regulated land uses that, for instance, generate non-point source pollution.

Environmental Policies Section 879 enables Official Community Plans (OCPs) to include “policies of the local government relating to the preservation, protection and enhancement of the natural environment, its ecosystems and biological diversity”.

Development approval information areas or circumstances (Section 879.1) enable the designation of areas or circumstances, or areas for which in specified circumstances, development approval information may be required.

Runoff Control Section 907 enables local governments to set maximum percentages of areas that can be covered by impermeable material and to set requirements for ongoing drainage management.

Landscaping Section 909 enables local governments to set standards for and regulate the provision of landscaping for the purposes of preserving, protecting, or restoring and enhancing the natural environment (e.g. requiring streamside vegetation).

Development Permit Areas Development permit areas designated in an Official Community Plan (see Section 919.1) cannot be altered, subdivided, or built on without a development permit. The permit can contain conditions for the protection of the environment.

Subdivision Servicing Requirements Section 938 enables a local government to “require that, within a subdivision”… “a drainage collection or a drainage management system be provided, located and constructed in accordance with the standards established in the bylaw”. In addition to the above, other stormwater management powers can be found in provisions dealing with building regulations, contaminated sites, development cost charges, ditches and drainage, dikes, development works agreements, flood protection, farming, highways, improvement districts and specified areas, park land, regional district services, sewage systems, subdivision, temporary commercia l and industrial use, tree cutting, utilities, water and waste management.

(Note: The section references quoted above are expected to change over time. Some of these changes will result from implementation of the Community Charter process in the near future.)


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1.5 History and Evolution of Stormwater Management The evolution of stormwater practice in North America is set against the backdrop of social change, and changes in stormwater management philosophy.

North American Context Modern urban stormwater infrastructure was born in the post-World War I era, consisting of efficient drainage systems with catch basins and pipes leading to the nearest stream.

Some time after World War II it became apparent to engineers throughout North America that the fruit of an efficient stormwater system was downstream flooding and channel erosion. By the early 1970s, this resulted in a new idea to solve flooding forever: on-site detention.

In the 1970s, the literature began to reflect a new concept: stormwater master planning. The idea was that engineers could construct a hydrology model (how much water, how often?) and a hydraulic model (how fast and high does the water from the hydrology model go?) of a watershed and then analyze scenarios until they found the perfect solution to flooding problems – whether current problems or those only imagined.

By the mid-1980s, literally hundreds of master plans had been developed. But few were being implemented the way they were planned. The cycle was one where local governments typically proceeded from flooding to panic to planning, and then to procrastination and the next flood.

In the late 1980s, a new breed of approaches emerged as water quality and bio-assessment were added to the mix. Each solved the immediate problem of the past paradigm and created a more insidious problem of its own. Knowledge and technology created a real or perceived need for higher, more demanding levels of stormwater management – and regulation.

The 1990s saw the introduction of ‘watershed-based’ approaches and ‘low impact development’.

Being aware of the changes in approach makes it increasingly less acceptable to do business as usual. The challenge ahead is to define and then actually demonstrate that a healthy watershed approach produces the full range of effective results in an efficient manner.


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British Columbia Context Before the 1970s, comprehensive urban drainage planning was a rarity in British Columbia, in part because there was no senior government funding for drainage projects. By the 1970s, however, drainage had emerged as an issue in the suburban areas because of flooding problems and resulting litigation. In the mid-1970s, the cities of Surrey, Nanaimo, West Vancouver (because of the July 1972 flooding that resulted in a catastrophic washout of the Upper Levels Highway during construction), and Kelowna were among the first municipalities to undertake major municipality-wide drainage studies. The history of modern stormwater management in British Columbia is summarized as follows: q A Flows-and-Pipes Approach

Master Drainage Plan (MDP) and Stormwater Management Plan (SMP) have tended to be used interchangeably in British Columbia over the past 25-plus years. A number of suburban municipalities (e.g. City of Surrey) continue to use the term MDP. The term SMP became popular in the late 1970s as ‘management’ became a catch-phrase for all infrastructure planning activities. The basic engineering approach did not materially change. Typically, an MDP was the ‘flows-and-pipes’ product resulting from a stormwater management strategy.

q An Environmental Approach In the 1989 through 1990 period, the City of Burnaby was the first municipality to apply what was initially called an ‘environmental approach’ to master drainage planning. This characterization reflected the evolution from a strictly engineering to an interdisciplinary team approach over a 6-year period for the Western versus Eastern Sectors, respectively, of the Big Bend Area in the Fraser River floodplain. The drivers for change were the impact of construction of the Marine Way arterial highway on existing market gardens, and the landfilling and conversion of undeveloped wetlands to industrial park uses.

q A Stream Stewardship Approach In 1992, the District of Maple Ridge adapted the Burnaby model in developing both a Stormwater Management Strategy and a Master Drainage Plan for the Cottonwood Area. At about the same time, the federal/provincial Land Development Guidelines and the provincial Urban Runoff Quality Control Guidelines were both published. Completed in 1994, the Cottonwood process showed how to make both sets of guidelines workable. The environmental agencies described it as a ‘stewardship template’ because it applied the concepts in the federal/provincial document titled Stream Stewardship: A Guide for Planners and Developers, also published in 1994.

q Higher Levels of Interdisciplinary Integration Integrated, ecosystem-based and watershed-based are terms that came into vogue at the end of the 1990s, and are interchangeable. Table 1-1 describes four case studies that took the Cottonwood template to successively higher levels of integration in terms of an interdisciplinary team approach. These case studies illustrate the transition from early environmental drainage to fully integrated stormwater management. They have given meaning to a comprehensive process for addressing hydrotechnical and environmental concerns in order to develop integrated solutions for the protection of property and habitat.

Integrated Stormwater Management Planning In British Columbia, the term Integrated Stormwater Management Plan (ISMP) has gained widespread acceptance by local governments and the environmental agencies to describe a comprehensive, ecosystem-based approach to stormwater planning.

The purpose of an ISMP is to provide a clear picture of how to be proactive in applying land use planning tools to:

q protect property from flooding, and q protect aquatic habitat from erosion and sedimentation

Use of the ISMP term is unique to British Columbia. The City of Kelowna first used the term in 1998 to make a clear distinction between ‘suburban watershed management’ and the Province’s existing ‘integrated watershed management’ process for natural resource management in wilderness watersheds. This is an important distinction. Local government typically has control over stormwater in residential, commercial and industrial land uses. It does not necessarily have control over watersheds.

Local governments in British Columbia are changing. Those that are changing are providing models for others to adapt and further evolve.


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Table 1-1 Origin and Evolution of Integrated Stormwater Management in British Columbia

Year Municipality Project Name and Relevance

1996 City of Kelowna Environmental Component of an Integrated Strategy for Stormwater and Stream Corridor Management:

The term ‘integrated stormwater management’ originated with the Kelowna study. This distinction was important to the City. It captured the essence of what the City was trying to accomplish through its 'environmental approach' to watershed protection.

In the Kelowna context, 'integrated' referred to the linkages between watershed actions and stream corridor consequences. The study was comprehensive in developing a science-based framework for broadly defining watershed management objectives for the City's nine drainage basins.

1997 City of Surrey Integrated Stormwater Management Strategy & Master Drainage Plan for the Bear Creek Watershed

The Bear Creek study was undertaken in parallel with Kelowna. It considered all the runoff events comprising the annual hydrograph. The emphasis was on how to integrate the range of hydrologic criteria for sizing of stormwater control facilities that have different functional objectives.

Two components were defined: 'hydro-technical' described the conventional engineering approach to conveyance of large runoff events; while 'enhanced hydro-technical' captured the environmental objectives in restoring the natural hydrology characteristic of the small runoff events.

Year Municipality Project Name and Relevance

1998 G.V.R.D

City of Burnaby

City of Coquitlam

City of Port Moody

Integrated Stormwater Management Strategy for Stoney Creek Watershed

The Stoney Creek study was an inter-municipal pilot project, and built on the base provided by the Kelowna and Bear Creek experiences. The emphasis was on consensus -building (through a workshop process) to develop a shared vision that integrated a range of diverse viewpoints on the 10-person Steering Committee that also included a community representative.

The foundation for strategy development was an assessment of the natural resources to be protected. The deliverables included a 20-Year Vision Plan and a 50-Year Vision Plan for stream preservation and watershed enhancement, respectively. These plans established targets for impervious area reduction.

2000 City of Coquitlam Como Creek Integrated Stormwater Management Plan – Flood Risk Management and Watershed Restoration

Como Creek took the Stoney process to the next level of detail. Como is the first urban drainage study in the Greater Vancouver region to truly integrate the engineering, planning and ecological perspectives through an inter-departmental, interdisciplinary and inter-agency process that was guided by a Steering Committee of senior managers, and that included community involvement in development of the resulting plan.

The goal was to develop an integrated plan that resolved a chronic flooding problem while over time restoring aquatic habitat. The focus was on how to implement changes in land use regulation that achieve the 50-year vision for impervious area reduction as the existing housing stock is replaced.


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Provincial Enabling Initiatives In 1992, the (then) Ministry of Environment, Lands and Parks published the Urban Runoff Quality Guidelines and the Guidelines for Developing a Liquid Waste Management Plan (LWMP).

In February 1994, the Ministry issued a policy statement to local government regarding the need to incorporate a stormwater component in LWMPs.

In July 1997, the Provincial Government enacted both the Local Government Amendments Act and the Fish Protection Act to give local governments new and improved tools to restore and enhance, as well as to protect, the natural environment.

In 1998, the Ministry published a document titled Tackling Non-Point Source Water Pollution in British Columbia - An Action Plan, which identified a series of tools and strategies available to reduce and prevent non-point source pollution in rural and urban areas.

The 1998 Non-Point Source Pollution (NPS) Action Plan The 1998 Action Plan comprises six initiatives. The one that is particularly relevant to this Guidebook is Land Use Planning, Coordination, and Local Action. This initiative addresses both stormwater management and streamside protection. Local governments that have LWMPs are required to incorporate a stormwater management component. LWMPs may themselves be required in critical areas where, for example, NPS pollution affects aquatic resources.

Initiatives at the Regional Level The Capital Regional District was the first jurisdiction to address stormwater quality in an LWMP for the Saanich Peninsula in 1996.

The Greater Vancouver Regional District formally embraced stormwater management in November 1994. This eventually led to formation of the inter-municipal and inter-agency Stormwater Task Group in 1997 to tackle stormwater quantity and quality issues. The ongoing role of this group is to formula te and guide implementation of a consistent regional approach to stormwater management planning as part of its LWMP.

Chapter Two

2.1 Developing a Common Understanding� Research on the Effects of Urbanization on Fish� A Science-Based Understanding

2.2 The Natural versus Urban Water Balance� Where Rainfall Goes Before and After Development� Distribution of Rainfall Over a Year� Role of Soil, Vegetation and Trees in Capturing Rainfall

2.3 Understanding Changes in Hydrology� Relationship Between Impervious Area and Runoff Volume� Other Hydrology-Based Relationships� Hydrology and Water Quality Objectives for Protection of Watershed Health

2.4 Factors that Limit the Health of Aquatic Resources� Ranking of Limiting Factors� Reference Impervious Area Levels for Land use Planning� Measuring the Environmental Health of Creek Systems� Other Washington State Research Findings

2.5 Managing Complexity� Eliminate the Source of Problems� What the Science is Telling Us� What Can be Done at the Site Level to Protect Watershed Health� Objectives for Protecting Watershed Health in an Urban Environment

The Science Behind IntegratedStormwater Management


STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIAPART A – WHY INTEGRATED STORMWATER MANAGEMENT?

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2.1 Developing a Common UnderstandingA science-based understanding of how land development impacts watershed hydrology andthe functions of aquatic ecosystems provides a solid basis for making decisions to guide earlyaction where it is most needed.

This chapter provides an overview of the science. It presents graphics that have helpeddiverse audiences reach a common understanding about hydrology and the factors limitingthe ecological values of streams.

An understanding of the science is a critical underpinning of strategies to predict and managethe potential impacts of stormwater related to land use change.

Research on the Effects of Urbanization on FishAquatic habitats that influence the abundance of salmon and trout are the outcome ofphysical, chemical and biological processes acting across various scales of time and space.The environmental conditions that result from these processes provide the habitatrequirements for a variety of species and life history stages of fish and other streamorganisms.

Decline of Wild SalmonWhether in pristine or heavily urbanized watersheds, the basic requirements for survival ofsalmon and trout are the same. These basic requirements include: cool, flowing water free ofpollutants and high in dissolved oxygen; gravel substrates low in fine sediment forreproduction; unimpeded access to and from spawning and rearing areas; adequate refuge andcover; and sufficient invertebrate organisms (insects) for food.

Over the past century, salmon have disappeared from over 40% of their historical range, andmany of the remaining populations are severely depressed (Nehlsen et al. 1991). There is noone reason for this decline. The cumulative effects of land use practices, including timberharvesting, agriculture and urbanization have all contributed to significant declines in salmonabundance in British Columbia (Hartman et al. 2000)

Puget Sound FindingsIn Puget Sound, a series of research projects have been underway for over 10 years to identifythe factors that degrade urban streams and negatively influence aquatic productivity and fishsurvival. The streams and sites under examination represent a range of developmentintensities from nearly undisturbed watershed conditions to watersheds that are almostcompletely developed in residential and commercial land uses (Horner 1998).

For each watershed, detailed continuous simulation hydrologic models were prepared andcalibrated to rainfall and runoff data. Physical stream habitat conditions, water quality,sediment composition, sediment contamination, and fish and benthic organism abundanceand diversity were measured and documented for each site.

The studies found that stream channel instability is a result of the urbanization of watershedhydrology. The alteration of a natural stream’s hydrograph is a leading cause of change ininstream habitat conditions. The physical and biological measures generally changed mostrapidly during the initial phase of watershed development, as total impervious area changedfrom 5% to 10%. With more intensive urban development in the watershed, habitatdegradation and loss of biological productivity continues, but at a slower rate (Horner 1998).

The role of large woody debris in streams was recognized as a key factor in creating complexchannel conditions and habitat diversity for fish. Both the prevalence and quality of largewoody debris declined with increasing urbanization. In addition, development pressure hashad a negative impact on streamside (riparian) forests and wetlands, which are critical tonatural stream functioning.

The impacts of poor water quality and concentrations of metals in sediments did not showsignificant impact to aquatic biological communities until urbanization increased aboveapproximately 50% total impervious area.

Instream habitat conditions had a significant influence on aquatic biota. Streambed quality,including fine sediment content and channel stability, affected the benthic macro invertebratecommunity (as measured by the multi-metric Benthic Index of Biological Integrity (B-IBI)developed by Karr (1991)). Negative impacts to fish and fish habitat from sedimentationrelated to urban development have been documented (Reid et al. 1999). The composition ofthe salmonid community was also influenced by a variety of instream physical and chemicalattributes.


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Summary of Puget Sound FindingsAlterations in the biological community of urban streams are a function of many variablesrepresenting conditions that are a result of both immediate and remote environmentalconditions in a watershed. The research findings clearly demonstrate that the most importantimpacts of urbanization that degrade the health of streams, in order of importance, are:

� Changes in hydrology� Changes in riparian corridor� Changes in physical habitat within the stream, and� Water quality

Further discussion of these impacts is contained in Section 2.4.

Georgia Basin FindingsWithin the Georgia Basin, population pressures have caused urban sprawl, resulting in habitatloss (B.C. MELP 2000). Freshwater fish population declines in this region are a partial resultof rapidly expanding urban development (Slaney 1996).

The aquatic ecosystems most directly affected by urbanization are the small streams andwetlands in the lowlands of the Georgia Basin and lower Fraser River Valley. Theseecosystems are critical spawning and rearing habitat for several species of native salmonids(both resident and anadromous). In the Lower Fraser Valley, 71% of streams are consideredthreatened or endangered, and a further 15% have been lost altogether as a result of urbangrowth (B.C. MELP 2000).

A Science-Based UnderstandingThe widespread changes in thinking about stormwater impacts that began in the mid to late1990s reflect new insights in two areas:

� Hydrology, and� Aquatic ecology

These new insights are the result of improved understanding of the causes-and-effects ofchanges in hydrology brought about by urban development, and the consequences for aquaticecology. As we gain new knowledge and understanding of what to do differently, a centralissue for watershed protection becomes:

� What is the proper balance of science and policy that will ensure effectiveimplementation and results?

King County in Washington State addressed this question in 1999 as part of the Tri-Countyresponse to the listing of chinook salmon as an endangered species in Puget Sound. Asignificant finding was that scientists and managers think and operate differently. This led tothe following recommendations:

� An interface is needed to translate the complex products of science intoachievable goals and implementable solutions for practical resource management.This interface is what we now call a science-based understanding.

� A reality for local government is that management decisions need to be made inthe face of significant scientific uncertainties about how exactly ecosystemsfunction, and the likely effectiveness of different recovery approaches.

� The best path forward is a dynamic, adaptive management approach that willallow local governments to monitor the effectiveness of their regulatory andmanagement strategies and make adjustments as their understanding grows.

� In a co-evolving system of humans and nature, surprises are the rule, not theexception; hence, resilience and flexibility will need to be built into themanagement system.

Through a science-based understanding of the relationship between hydrology and aquaticecology, this chapter derives a comprehensive set of watershed protection objectives thatprovide an over-arching framework for Parts B and C of this Guidebook.


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2.2 The Natural versus Urban Water BalanceRainfall landing on a site travels in four directions:

� Soaking into shallow ground and moving slowly through soils to streams -interflow

� Percolating vertically into deep groundwater� Back up into the air – evaporation from surfaces and transpiration from leaves -

evapotranspiration� Flowing over the ground – surface runoff

Because the total volume of rainfall equals the sum of the four components, this relationshipis known as the ‘Water Balance’. It is a core hydrologic concept.

Urban drainage has traditionally focused on managing surface runoff. It is only recently thatthe other three components have begun to receive serious attention, with the emphasis oninterflow. Although interflow was first defined in the 16th century, its significance has beenlargely ignored for over 400 years. It is now recognized that all four components need to beconsidered as part of a comprehensive and integrated approach to stormwater volumemanagement.

Where Rainfall Goes Before and After DevelopmentFigure 2-1 illustrates how the Water Balance changes when natural vegetated cover isreplaced by suburban development. By providing example percentages, this drawinghighlights the magnitude of the additional volume of water that must be handled by adrainage system after land is cleared. The actual percentages will vary from region to region,but the relationships are universal.

On an annual basis, surface runoff from a forested or naturally vegetated watershed in thePacific Northwest is minimal as a proportion of total water volume. Before development, theflow that we observe in streams is actually interflow. After development, flow in streamstypically originates as surface runoff.

As a watershed is cleared, surface runoff volume increases in proportion to the percentage ofimpervious surface area, defined as non-infiltrating surfaces (e.g. concrete, asphalt, rooftops,

hard landscaping and exposed rock). Once a pipe system is installed to drain theseimpervious areas, almost every rainfall results in runoff.


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Figure 2-1


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Distribution of Rainfall Over a YearUnderstanding how rain falls over the course of a year is fundamental to understanding theWater Balance and how to manage its components. Figure 2-2 is an example of a typicaldistribution of annual rainfall volume. While total rainfall can vary significantly betweenregions, the distribution pattern is universal for British Columbia.

Note: approximate percentages based on casestudy experience from the Georgia Basin

75%

20%

5%

frequently occuring small storms

infrequent large storms

rare extreme storms

Rainfall Event Size

Less than 30mm From 30mm to 60mm Greater than 60mm

Role of Soil, Vegetation and Trees in Capturing RainfallThe relevance of Figure 2-2 is in making the case that the frequently occurring small rainfallevents hold the key to protecting the Water Balance in the urban environment. Small rainfallevents typically account for 75% of the annual rainfall volume.

Because the majority of rain falls in small amounts, soil and vegetation are generally able toabsorb and infiltrate it as it falls – this is why interflow and evapotranspiration are maximizedand surface runoff is minimized in a forested environment.

In a natural condition, vegetated surface soil layers are highly permeable. As surface plantsdie and decompose, they provide a layer of organic matter which is stirred and mixed into thesoil by earthworms and microbes. This soil ecosystem provides high infiltration rates and abasis for interflow.

Trees contribute to the soil ecosystem in two ways: the root zone creates a permeableenvironment; and the buildup of forest litter creates an absorbent layer.

In an urban situation, preservation and/or restoration of soil, vegetation and trees can help to:

� Recharge interflow� Protect baseflow� Minimize runoff

Water Balance Objectives for Protecting Watershed HealthIn terms of preventing land development and related human settlement activities in the urbanenvironment from impacting the Water Balance, British Columbia case study experience hasresulted in identification of the following objectives for a truly healthy watershed:

� Objective 1 - Preserve and protect the water absorbing capabilities of soil,vegetation and trees.

� Objective 2 - Prevent the frequently occurring small rainfall events frombecoming surface runoff.

Figure 2-2


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2.3 Understanding Changes in HydrologyStormwater management practitioners now commonly use the phrase ‘changes in hydrology’.Figure 2-3 presents a basic definition of this phrase:

Relationship Between Impervious Area and Runoff VolumeFigure 2-4 illustrates the progressive changes in hydrology that result when land use changealters the Water Balance. Replacement of natural vegetation and soil with impervioussurfaces reduces infiltration and evapotranspiration. The total runoff volume increases (asshown in red), and so does the Mean Annual Flood (MAF), a statistical rating of the annualpeak flows in a creek system.

The MAF is defined as the channel-forming event because the cross-sections of streamchannels tend to reach equilibrium with the MAF. When the MAF increases, the channelerodes to expand its cross-section. A critical parameter for watercourse erosion is the numberof runoff events per year that equal or exceed the natural MAF. The more frequently thenatural MAF is exceeded, the greater the channel instability, leading to habitat degradation asa result of erosion and sedimentation.

A second critical parameter is the ratio of the MAF to the winter baseflow. Washington Stateresearch indicates that 20:1 is a threshold ratio for coastal fisheries biodiversity andabundance.


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Figure 2-4


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Other Hydrology-Based RelationshipsImpervious Area and Water QualityNot only does more impervious surfaces mean more runoff volume, it also means there ismore surface area (e.g. roads, parking lots) available to collect pollutants which then wash offinto receiving streams when it rains. Most stormwater runoff receives no treatment before itis discharged to streams.

More runoff volume also means there will be more instream erosion and more frequentturbidity (or dirty water).

Another measure of changes in hydrology is the level of total suspended solids (TSS) in acreek system. TSS comprises the direct wash-off from impervious surfaces, plus sedimentthat erodes from stream bottoms and sides. TSS acts as a carrier of other pollutants such asorganics, hydrocarbons and metals.

Interflow and BaseflowYet another measure of changes in hydrology is the Mean Annual Discharge (MAD). This isthe average flow over the year. MAD is applied when assessing the relative magnitude ofsummer baseflows.

The interflow component of the Water Balance sustains baseflow. In fact, interflow can keepcreeks flowing for months after winter rainfall stops. Interflow recharge depends on theintegrated hydrologic function of soil, vegetation and trees. If interflow is reduced, baseflowis reduced.

When considering both community water supply and fisheries needs during periods ofprolonged dry weather, a generally accepted criterion in British Columbia for Water Balanceassessment purposes is that minimum baseflows should equal 10% of MAD.

Hydrology and Water Quality Objectives for Protecting Watershed HealthIn terms of mitigating the impacts of impervious area on watershed hydrology, BritishColumbia case study experience has resulted in identification of the following hydrology-based objectives for a truly healthy watershed:

� Objective 3 – Provide runoff control so that the Mean Annual Flood (MAF)approaches that for natural conditions.

� Objective 4 – Minimize the number of times per year that the flow ratecorresponding to the natural MAF is exceeded after a watershed is urbanized.

� Objective 5 – Establish a total suspended solids (TSS) loading rate (i.e.kilograms per hectare per year) that matches pre-development conditions.

� Objective 6 – Maintain a baseflow condition equal to 10% of the Mean AnnualDischarge (MAD) in fisheries-sensitive systems.


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2.4 Factors that Limit the Health of Aquatic Resources

A science-based understanding of the factors that limit the health of aquatic resources leads toreference levels of impervious area for planning purposes. This understanding provides thebasis for setting performance targets and developing site design criteria.

Ranking of Limiting FactorsResearch by the University of Washington (Horner and May 1996) clearly demonstrated thatthe factors limiting the ecological values of urban streams are, in order-of-priority:

1. Changes in Hydrology –Greater volume and rate of surface runoff caused by increased impervious areaand densification of the road network.

2. Disturbance and/or Loss of Integrity of the RiparianCorridor –Clearing and removal of natural vegetation in riparian (streamside) areas.

3. Degradation and/or Loss of Aquatic Habitat within theStream –

Caused by erosion and sedimentation processes, bank hardening, and removal oflarge organic debris; aquatic habitat degradation is a direct result of changes inhydrology (Factor #1).

4. Deterioration of Water Quality –Increased sediment load due to more runoff volume causing channel erosion.Pollutant wash-off from land uses, deliberate waste discharges and accidentalspills.

Figure 2-5 illustrates the research findings for two of these factors: changes in hydrology (#1)and deterioration in water quality (#4).

The work of Horner and May has had a profound impact in changing the way stormwaterprofessionals view the relationship between watershed impervious area and stream health.

Their work has also resulted in a science-based understanding that, in turn, has enabled thedefinition of reference levels for land use planning.

At 10%, biodiversity and abundance initially impacted

By 30%, most urban watersheds may beunable to sustain abundant self-supportingpopulations of cold-water fish

B-IBI = 30 is thethreshold level forcreek health

Acute aquatic life criterion

Fish would already be gone by thetime pollutant loading is a factor infish survivability

Chronic aquatic life criterion

HydrologyThreshold @ 30%

Water QualityThreshold @ 60%

1

1

20

25

30

35

40

45

1 20 30 40 50 60 70Total Impervious Area (%)

Creek Health (B-IBI) Versus Impervious Land Cover

Water Quality Versus Watershed Impervious Land Cover

50

20

1

40

30

70

60

Total Impervious Area (%)201 30 40 50 7060

Reference Levels for Land Use Planning


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Figure 2-5

Reference Impervious Area Levels for Land use PlanningThe scientific correlations presented on Figure 2-5 are simplified in the table below. Theobjective is to provide points of reference for integration of stormwater management withland use planning. This simplification will at least enable informed decision making. Inreality, land use and stream health changes occur along a continuum.

ImperviousPercentage

Biophysical Significance of the Reference Level

10% Fisheries biodiversity and abundance are initially and significantly impacted

30% Most urban watersheds in the Pacific Northwest may be unable to sustainabundant self-supporting populations of cold-water fish

60% Pollutant loading would theoretically be a significant factor in fish survival,except cold-water fish would likely already have been extirpated because ofhydrological changes and related degradation of the aquatic habitat

Measuring the Environmental Health of Creek SystemsFigure 2-5 refers to a Benthic Index of Biological Integrity (B-IBI) score as an indicator ofcreek health. B-IBI is a multimetric benthic macroinvertebrate index designed and calibratedfor use in the Pacific Northwest. Each of the metrics it incorporates (e.g. total number oftaxa, number of pollution tolerant taxa) was chosen for its consistency in responding toseveral types of human disturbance, including urbanization, forestry, agriculture andrecreation. B-IBI is also useful because it is very sensitive to slight changes in a watershed.

Benthic invertebrates are used because anadromous fish species in the Pacific Northwest aresubject to significant environmental pressures unrelated to their home watershed. Theseoutside influences affect their distribution, diversity and abundance, making it difficult to usefish population measures as indicators of stream health.

Other Washington State Research FindingsRiparian Corridor IntegrityIn any given watershed or at any given site, any one of the four factors can limit biologichealth. Research by the University of Washington (Karr and Morley 1999) as well as a seriesof studies summarized by Millar (1997) demonstrate the importance of healthy ripariancorridors. The presence or absence of healthy riparian forest greatly affects a stream’sbiologic integrity in otherwise similar watersheds with similar total imperviousness.

A healthy, forested riparian corridor can partially compensate for impervious surfaces in awatershed. In contrast, a cleared riparian corridor results in a damaged stream even in awatershed with low impervious area.

Density of Road NetworksAnother significant finding is that the density of road networks also provides an excellentway to closely track total impervious area and associated impacts. This is because of thedrainage system pattern associated with nearly all roads.

Drainage ditches collect surface water and interflow and transport it immediately to streams.Resulting changes in stream-system hydrology are similar to the effects of increasedimpervious surfaces.

Biophysical Objectives for Protecting Watershed HealthIn terms of preventing changes in hydrology from impacting aquatic resources, WashingtonState research has resulted in identification of four objectives for defining a truly healthywatershed – that is, one that can support self-sustaining populations of wild salmon:

� Objective 7 - Limit impervious area to less than 10% of total watershed area.

� Objective 8 - Retain 65% forest cover across the watershed.


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2.5 Managing Complexity

There is a logical link between changes in hydrology and impacts on watershed health, whether those impacts are in the form of flooding or aquatic habitat degradation. The link is the volume of surface runoff that is created by human activities as the result of alteration of the natural landscape (i.e. through removal of soils, vegetation and trees).

Eliminate the Source of Problems The key to protecting watershed health is to maintain the Water Balance as close to the natural condition as is achievable and feasible. But protecting the interflow and evapo-transpiration components requires major changes in the way we develop land (i.e. if we are to preserve and/or restore soils, vegetation and trees). Understanding the cause-and-effect relationship between hydrology and biology provides credibility for a change in approach from only dealing with consequences, to also eliminating the source of problems. This shift in thinking is illustrated by Figure 2-6 below.

Science-based credibility helps people accept new ways of thinking. But to maintain credibility, it is important to apply common sense to the science.

Figure 2-6

What the Science is Telling Us The science is explicitly telling us that major biophysical changes occur once the impervious percentage of a watershed reaches about 10%. Beyond this threshold, the change in the Water Balance triggers watercourse erosion, which in turn degrades and/or eliminates aquatic habitat.

The science is implicitly telling us that where urban land use densities are produced, the focus should be on what needs to be done at the site level to effectively mimic a watershed with only 10% impervious area, and in doing so reduce runoff volume to the same 10% level.

The science is also implicitly telling us that capturing rainfall at the source for the frequent small events will in large part maintain or restore the natural Water Balance.

What Can be Done at the Site Level to Protect Watershed Health The financial and staff resources of local government are limited. Therefore, those resources must be invested wisely to maximize the return-on-effort. Common sense says that the best return will be at the site level where local government exerts the most influence, and can therefore make a cumulative difference at the watershed scale.

A Starting Point for Early Action Common sense says that we now have sufficient science-based knowledge and understanding for local government to make some decisions, and to get on with implementing early action in at-risk areas. More data to refine the science is desirable when there is time and resources, however, there will be situations where excessive data collection becomes a barrier to effective action in the face of an immediate risk.

Strategic data collection required is to understand the historic Water Balance, the current Water Balance if the watershed is partially developed, and the proposed changes to land use in the watershed.

Looking ahead to the discussion in Parts B and C, the objectives of most ISMPs will include trying to maintain or restore the natural Water Balance as development or re-development proceeds. Improved understanding of how to do that will evolve through demonstration projects that test and refine solutions to aquatic habitat and receiving water quality challenges.


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A Starting Point for Early ActionCommon sense says that we now have sufficient science-based knowledge and understandingfor local government to make some decisions, and to get on with implementing early actionin at-risk areas. More data to refine the science is desirable when there is time and resources,however, there will be situations where excessive data collection becomes a barrier toeffective action in the face of an immediate risk.

Strategic data collection required is to understand the historic Water Balance, the currentWater Balance if the watershed is partially developed, and the proposed changes to land usein the watershed.

Looking ahead to the discussion in Parts B and C, the objectives of most ISMPs will includetrying to maintain or restore the natural Water Balance as development or re-developmentproceeds. Improved understanding of how to do that will evolve through demonstrationprojects that test and refine solutions to aquatic habitat and receiving water qualitychallenges.


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Objectives for Protecting Watershed Health in the Urban EnvironmentThe three sets of objectives for a truly healthy urban watershed are brought forward from theprevious sections and consolidated below. The purpose is to provide an integratedframework for guiding the actions of local governments within their sphere of responsibilityand influence.

Water Balance� Objective 1 - Preserve and protect the water absorbing capabilities of soil,

vegetation and trees.

� Objective 2 - Prevent the frequently occurring small rainfall events frombecoming surface runoff.

Hydrology / Water Quality� Objective 3 – Provide runoff control so that the Mean Annual Flood (MAF)

approaches that for natural conditions.

� Objective 4 – Minimize the number of times per year that the flow ratecorresponding to the natural MAF is exceeded after a watershed is urbanized.

� Objective 5 – Establish a total suspended solids (TSS) loading rate (i.e.kilograms per hectare per year) that matches pre-development conditions.

� Objective 6 – Maintain a baseflow condition equal to 10% of the Mean AnnualDischarge (MAD) in fisheries-sensitive systems.

Biophysical� Objective 7 - Limit impervious area to less than 10% of total watershed area.

� Objective 8 - Retain 65% forest cover across the watershed.

� Objective 9 - Preserve a 30-metre wide intact riparian corridor along allstreamside areas.

� Objective 10 - Maintain B-IBI (Benthic Index of Biological Integrity) scoreabove 30.


The Scope of Integrated Stormwater Management Chapter Three

3.1 Overview and Context� Connecting the Natural and Built Environments� Integration Means Tackling Water Quantity and Water Quality� Blending Policy, Science and Site Design

3.2 The Transition from Traditional to Integrated Stormwater Management� Evolution of the Integrated Approach� Change in Approach: from Reactive to Proactive� Volume Reduction is the Key to Property and Environmental Protection� The Evolving Role of Governments in Integrated Stormwater Management

3.3 Plan at Four Scales – Regional, Watershed, Neighbourhood and Site� What the Cell is to the Body, the Site is to the Region� Cascading Hierarchy of Integrated Solutions

3.4 Integrated Stormwater Management Planning� Producing a Shared Vision� An Action Plan with Four Components

3.5 The Relationship between Stormwater and Land Use� Ten Principles

3.6 A Guide to Part B� Case Studies

STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIAPART B – INTEGRATED STORMWATER MANAGEMENT SOLUTIONS


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3.1 Overview and Context

An integrated approach recognizes that land use changes outside a stream corridor result inchanges within the corridor. The impact of land development in changing both stormwaterquantity and quality can trigger progressive loss of biodiversity and abundance of aquaticspecies within the corridor.

Connecting the Natural and Built EnvironmentsIntegrated, or watershed-based, stormwater management recognizes the relationships betweenthe natural environment and the built environment, and manages them as integratedcomponents of the same watershed. These relationships are illustrated in Figure 3-1.Traditional drainage practices concentrated on peak flow rates and overlooked the importanceof volume management. Integrated solutions manage both volume and flow rates.

Integration Means Tackling both Stormwater Quantity and QualityIntegrated stormwater management includes attention to both stormwater quality andquantity. Water quality impairments correlate with increased watershed percentimperviousness, as well as with increased population density. Rainfall washes fine sedimentfrom hard surfaces into piped systems that discharge into receiving waters. As an areadevelops, the total volume of sediment loading increases.

The majority of trace metals and hydrocarbons, for example, are associated with suspendedsediment. Hence, it is common sense that reducing stormwater volume will also reducesediment loading and reduce aquatic pollution. When stormwater is infiltrated through soil,many sediment-bound contaminants are removed by filtration. Similarly, constructedwetlands can also act as settling ponds to remove and treat suspended sediments in runoff.Other stormwater treatment technologies are available commercially and may becomeimportant as development intensifies.

Programs that increase public awareness of common non-point source pollutants in the homeand business will also contribute to reduced pollutant loads. Other more rigorous sourcecontrol programs (e.g. bylaws) may also become necessary as land use intensifies.

Trees, vegetation, and naturalsoils evaporate, absorb andinfiltrate water

Roofs, pavement, and hardlandscaping preventinfiltration of runoff andconcentrate flow

Rainfall is transformed intoINTERFLOW (not surfacerunoff)

Rainfall is transformed intoInterflow and Surface Runoff

Headwater streams extendinto the upper extremities of awatershed

Headwater streams are replacedby man-made infrastructure(ditches/pipes)

Figure 3-1


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Blending Policy, Science and Site DesignIntegrated stormwater management blends policy, science and site design through anintegrated approach. Key steps are:

� Policy –Identify goals, objectives, locations and guidelines for both land use development andstormwater management. Organize priorities and financial and administrative support.

� Science –Build a science-based understanding of the link between urban development impacts,stream degradation, and other policy objectives. This understanding leads to realisticperformance targets and design criteria for each watershed catchment.

� Site Design –Identify site design practices that support the policy objectives and meet the performancetargets. Once identified, these site design practices must be allowed and supported at thepolicy level. Changes to development standards and regulations are also needed toenable better site design practices.

Policy, science and site design are blended through a participatory and interactive processwhere technical products are developed and presented at a series of working sessions withstakeholders. The objective is to reach consensus on a shared vision that is practical andachievable, and that will be supported by the community. Community support is the key tomoving from planning to action. Chapter 11 elaborates on this topic.


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3.2 The Transition from Traditional toIntegrated Stormwater Management

Evolution of the Integrated ApproachStormwater management has evolved over the decades, and continues to evolve. Thefollowing comparison captures the key elements of the transition from a traditional, 1980sapproach, to an integrated approach in the 2000s. The integrated approach still incorporatesthe traditional scope of engineering work, but builds on it to achieve environmental as well asdrainage objectives, as the following table demonstrates:

TRADITIONAL is defined as:

� Drainage Systems� Reactive (Solve Problems)� Engineer-driven� Protect Property� Pipe and Convey� Bureaucratic Decisions� Local Government Ownership� Narrow Scope of Work (drainage focus only)

INTEGRATED is defined as:

� Ecosystems� Proactive (Prevent Problems)� Interdisciplinary Team-driven� Protect Property and Resources� Mimic Natural Processes� Consensus-based Decisions� Partnerships with Others� Holistic Scope of Work

(stormwater integrated with land use)

An integrated approach to stormwater planning is inter-departmental, interdisciplinary andinter-agency. It also involves community representatives in the planning process. Theseelements and their significance are explained in later chapters in Part C.

Change in Approach: from Reactive to ProactiveIntegrated stormwater solutions ensure protection of both property and ecosystems. Pastdrainage practices only dealt with the consequences of land development. An integratedapproach also attempts to eliminate the source of problems.

Figure 3-2 illustrates what is involved in moving from an ‘end-of-pipe’ approach that solvesproblems after the fact, to one that is proactive in preventing problems from occurring.

the reason to change

what to change

agreeing to change

making the change

Figure 3-2


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Volume Reduction is the Key to Property and Environmental ProtectionTo avoid aquatic habitat and water quality impacts and protect property, it is necessary todecrease the volume of runoff that flows to streams, thereby creating a situation that mimicsor approximates a naturally vegetated watershed. Past stormwater management practices didnot accomplish this because they focused only on the conveyance and/or detention of theextreme storms.

Extreme storms occur rarely. Because the small, frequently occurring rainfall eventsrepresent the bulk of total rainfall, the key to runoff volume reduction is to capture thoseevents at the source. If they can be captured and restored to their natural hydrologicpathways (through infiltration and re-use within a development site), then the majority of thetotal annual rainfall will be managed in a manner approximating a natural system.

Strategies to Reduce Runoff Volume and Flow RateIntegrated solutions reduce the volume and the rate of surface runoff from the builtenvironment by a combination of three strategies:

� Minimize creation of impervious area, e.g. by using pervious surfaces, narrowerroads, skinny buildings, etc.

� Install hydraulic disconnects that return local runoff from impervious surfaces backinto the ground or re-use it within the development site.

� Store runoff and release it slowly. Ideally this storage would discharge to aninfiltration device prior to discharge to a watercourse.

In summary, integrated stormwater management recognizes that flood control, protection ofaquatic habitat and improvement of water quality are all complementary objectives. They allhave the same starting point – increased impervious area leads to increases in runoff.

The Evolving Role of Governments in Integrated Stormwater ManagementThe goal in BC is to develop integrated stormwater solutions that will ensure protection oflife, property, aquatic habitat and water quality. Achieving this goal requires alignment of theroles and responsibilities of the different levels of government.

Local government has responsibility for land use decisions. Local government is alsoresponsible for protection of property. Because of the direct relationship between land usedevelopment and stormwater impacts, local government must play a primary role in aquatichabitat protection and restoration related to stormwater management.

Recent changes to the Local Government Act have expanded the mandate for municipalitiesand regional districts to manage runoff and impervious area.

In view of the expanding role of local governments in stormwater management, a keyobjective of the Guidebook is to provide a pragmatic, integrated and science-based approachto stormwater planning. This will enable local governments and landowners to make long-term land use and development decisions with more confidence.

Providing Economy and Certainty During a Period of TransitionDuring this period of transition from traditional drainage practice to integrated stormwatermanagement, there is uncertainty as to what roles various levels of government and theprivate sector should play in stormwater management, and who pays.

Part C of the document suggests partnerships among various levels of government. Seniorgovernments recognize the importance of being proactive in developing strong and lastingpartnerships with local governments.

The Guidebook presents an adaptive methodology for moving from planning to action. Thismethodology focuses the limited financial and staff resources of governments onimplementing early action where it is needed most. It explains how to select conservativestrategies to guide early action. It also provides a framework for reducing the costs of thesestrategies through ongoing monitoring and evaluation.


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3.3 Plan at Four Scales – Regional, Watershed,Neighbourhood and Site

What the Cell is to the Body, the Site is to the RegionJust as the health of the human body is dependent on the health of the individual cells in it, sotoo is the health of the suburban region dependent on the health of the individual site – this isan over-arching theme.

A guiding principle is to plan at four scales to ensure that solutions are both integrated andcascading. The scales are the region, watershed, neighbourhood and site, as shown in theadjacent table.

Cascading Hierarchy for Integrated SolutionsThe objectives for stormwater management are referenced to, and defined by, the cascadinghierarchy shown to the right. Each successive level provides more specific details as to whatis to be accomplished, and how to achieve a shared community vision for the region and/orwatershed.

The planning scales are not mutually dependent. However, they work best when undertakentogether. In the context of this Guidebook, watershed-based planning means that resource,land use, and community design decisions are made with an eye towards their potentialimpact on the watershed or drainage catchment. Therefore, what happens at the scale of theindividual parcel and street affects what happens at the watershed scale.

PlanningScale

Description of Initiative Opportunity for ImplementingStormwater Management

Regional Regional Growth Strategy Provide local government withenabling tools

Regional Stormwater Component ofLiquid Waste ManagementPlans (LWMPs)

Prioritize limited resources on keyenvironmental stewardship issues

Regional Official Community Plan (OCP) Define over-arching community goalsand objectives

Watershed Watershed-Based Land UsePlanning Process

Develop a stewardship-based‘watershed vision’ that reflects OCP

Watershed Integrated StormwaterManagement Plan (ISMP)

Protect property, aquatic habitat andwater quality

Neighbourhood Neighbourhood CommunityPlan (NCP), orLocal Area Plan (LAP)

Establish performance targets forsubdivisions and site design

Site Subdivision and Single LotDevelopment Plans

Implement performance targets forsite design


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3.4 Integrated Stormwater Management PlanningThe evolving science of stormwater management has broadened the traditional engineeringapproach to one that integrates hydrologic and environmental concerns, and that is alsoproactive in managing risk. Hence, the term Integrated Stormwater Management Plan(ISMP) is gaining widespread acceptance in BC because it addresses two categories of riskmanagement:

� Flood Risk – to protect life and property� Environmental Risk – to protect habitat and property

Producing a Shared VisionTo address stormwater issues, it is critical that key stakeholders have a shared vision of thescience and the appropriate solutions for the watershed under consideration. Stakeholdersmust understand that land use change alters the natural Water Balance, that the result is moresurface runoff, and that the increase in both volume and flow rates has consequences.

The purpose of an ISMP is to create a clear picture of a desired outcome that will facilitate abroad understanding of integrated solutions – why they are needed, what they are, and howthey can be practically and affordably accomplished. An ISMP implementation program willorganize a transition from existing to revised standards that achieve the desired outcome.

An Action Plan with Four ComponentsFigure 3-3 illustrates how a process produces a shared vision that results in an action planwith four component plans. Chapter 10 elaborates on the concepts presented in this section.

The effectiveness of flood risk and environmental risk management depends on a LandDevelopment Action Plan that integrates decisions about land use and on-site stormwaterbest management practices to protect and/or restore the natural Water Balance.

The purpose of a Flood Risk Mitigation Plan is to protect life and property. This is achievedby containing and conveying the floodflows that result from the extremely large rainstormsthat rarely occur. This component has historically been called a Master Drainage Plan.

The purpose of a Habitat Enhancement Plan is to address environmental risk (to aquatichabitat and water quality). This means protecting stream corridor ecosystems from beingprogressively degraded by the erosion and sedimentation that result from the small rainfallevents that occur all the time. This is achieved through a combination of retention (rainfallcapture at the source) and detention (runoff control) strategies. This combination alsoindirectly addresses risks to water quality.

The purpose of a Financial and Implementation Plan is to provide cost sharing and control,funding and organization of the stakeholders to ensure effective implementation, monitoring,operating and maintenance.

Figure 3-3


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3.5 The Relationship between Stormwater and Land UseAs introduced in Chapter 2, the impacts of increasing impervious area on stream flows andfish habitat are cumulative. Changes in land use designations and zoning should considerhow much change to effective impervious area is encouraged by the proposed land use.

Table 3-1 shows a typical, generalized relationship between imperviousness and land use,without mitigation by best management practices (BMPs). This illustrates how the area perdwelling unit decreases with density. For example, the impervious area per dwelling unit fora high-density multi-family development is about 1/8 of the per unit area for a 1960ssuburban residential development.

Table 3-1 Presumed Relationship between Impervious Area and Land Use (1)

Land Use Density(units /acre)

TIA(percent)

EIA(percent)

Land/1000Dwellings

(acres)

EIA / 1000Dwellings

(acres)Rural Residential 0.5 10 4 2000 80Estate Residential 1 20 10 1000 1001960s Suburban 4 35 24 250 601990s Suburban* 5 55 45 200 90Low Multi-family 8 60 48 125 60High Multi-family**(underground parking)

50 60 48 20 10

Commercial/Industrial n/a 90 86 n/a n/a

(1) Extracted from Dinicola, 1989, Jackson and Booth, 1997TIA = total impervious area and EIA = effective impervious area (i.e. directly connected to drainage system)Refer to Chapter 6 for additional explanation regarding TIA versus EIA* Source: Como Creek watershed, City of Coquitlam – airphoto interpretation** Source: Burnaby Mountain Community, City of Burnaby – neighbourhood plan

Ten PrinciplesAn improved understanding of the relationship between stormwater management and landuse is important to make the case for closer integration of OCP and ISMP processes, and tobreak down barriers between planners and engineers. Table 3-2 identifies ten principles thathelp define the relationship between stormwater management and land use.

Looking ahead to Chapters 6 through 8, understanding the relationship between stormwaterand land use is also important in deciding when, where and how stormwater managementperformance targets should be applied.


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1. 10% impervious area is a critical threshold - Stormwater impacts increasedramatically when land use creates over 10% impervious area in a watershed or drainagecatchment.

2. Residential development has the greatest overall impact - Residential developmentoften has the greatest cumulative impact on stormwater management because it covers thegreatest land area.

3. Greater population = greater impact - The higher the population accommodated in awatershed or sub-watershed, the higher the likely water quantity and water qualityimpacts.

4. Same population, greater density = less impact - The greater the density ofresidential land use in a watershed for a given population, and the more remainingvegetated green space, the lower the likely stormwater impact.

5. Rule of thumb is to maintain catchment effective impervious area (EIA) below 10% -Generally, stormwater best management practices (BMPs) to manage flows should betriggered for all developments that involve more than 10% total impervious area. Theobjective of the BMPs would be to reduce the effective impervious area, and to meetdesignated targets for rainfall capture and runoff control.

6. BMPs are needed for residential densities exceed 1 unit per hectare - Mostresidential developments of densities greater than 1 unit per hectare will exceed the 10%impervious area trigger.

7. Industrial/commercial = greatest impervious area - Medium density commercial andindustrial developments have high impervious area that needs to be mitigated. However,these developments often represent a small portion of the watershed when compared toother land uses (e.g. residential).

8. Large structures in forestry/agricultural areas may require mitigating BMPs - Verylow density land uses such as agriculture or forestry will often have impervious area lessthan 10%, but can still have a major impact on watershed hydrology due to theconsequences of clearing and ditching. In addition, local sites such as greenhouses ortemporary industrial operations may trigger the need for specific stormwater managementmeasures. At the same time, drainage from upland urban areas may have floodingimpacts on agricultural lowland uses if not mitigated.

9. The impacts of impervious area are cumulative – An existing development that is notcreating a problem may contribute to a future problem as adjacent development infills.For this reason, all development with >10% EIA should implement stormwatermanagement, except in isolated cases where there is no likelihood of the total imperviousarea in a drainage catchment exceeding 10% (e.g. in completely rural areas).

10. Compact communities are most compatible with stormwater objectives - Themost favorable land use pattern for minimum stormwater impacts is compact, dense,pedestrian-oriented development with effective stormwater BMPs, and with the majorityof the watershed in vegetation and absorbent soils.

Table 3-2: Ten Principles that Define the Relationship between Stormwater Management and Land Use


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3.6 A Guide to Part BOften it is the small or tributary drainage catchments that are heavily impacted by land usechange. Since development activities can quickly transform a large portion of these at-riskcatchments, it is important that integrated stormwater management programs be put in placequickly. Priority action in at-risk catchments has several advantages:

� Demonstrates that local government is taking immediate action

� Focuses attention on the types of stormwater problems that will have to beaddressed in other areas

� Serves as a demonstration project for testing the effectiveness (and affordability)of stormwater management policies and techniques

Looking ahead, Chapter 4 describes two tools that can be used by local government to bringabout policy changes that will result in integrated solutions.

Chapter 5 describes an approach for setting priorities for early action. This is called the At-Risk Methodology (ARM). This methodology relies on a roundtable process that bringstogether people with knowledge about future land use changes, high-value ecologicalresources, and locations that have chronic drainage problems. The Regional District ofNanaimo is the case study example.

Chapters 6 through 8 then lead the reader through a step-by-step discussion on the selectionand application of achievable performance targets. Each chapter is a building block in asystematic process for translating performance targets into design criteria that can beimplemented at the site level to achieve watershed objectives. The City of Chilliwack and theGreater Vancouver Regional District (GVRD) are the case study examples.

� Chapter 6 explains how science-based performance targets have been set for theCity of Chilliwack, and shows how these targets have been translated into designcriteria.

� Chapter 7 then demonstrates how Chilliwack has integrated performance targetswith stormwater management policies.

� Finally, Chapter 8 illustrates how Chilliwack has incorporated performancetargets into a set of Design Guidelines for Stormwater Systems that developerscan understand and apply at the site level.

Case StudiesThe targets, criteria, policies and guidelines are incorporated in the City of Chilliwack’sPolicy and Design Criteria Manual for Surface Water Management. This Manual has beendeveloped as a case study application of the Guidebook content.

The GVRD case study (also presented in Chapter 8) evaluates a broad range of stormwatersource control options that can be applied to achieve performance targets.

Chapter Four

4.1 Policy Tools for Implementing Integrating Stormwater Management Solutions� Official Community Plans (OCPs)� Liquid Waste Management Plans (LWMPs)� Case Study Applications� Integrating Stormwater and Land Use Strategies

4.2 Liquid Waste Management Plans� Stormwater Management Role of Regional Districts� Relationship Between LWMP and ISMP Processes� ISMP Technical Products

4.3 Relationship Between OCPs and LWMPs� An OCP Provides the Foundation for an LWMP� Take Whatever Step Comes First� The Link Between Land Development and Stream Protection

4.4 Stormwater Management Goals, Objectives and Policies� Case Study Example: Customizing a Framework

4.5 Policy Transition in a Rural Regional District� Case Study Example: A Five Year Stormwater Management Program� The Need for Stormwater Management in Rural Regional Districts� Focusing Rural Stormwater Planning Efforts� An Action Plan for the Transition to Stormwater Management� Administering the RDN Stormwater Management Program� Partnerships for the RDN Stormwater Management Program

Policies for Integration of Land Use Planningand Stormwater Management



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4.1 Policy Tools for Implementing Integrated StormwaterManagement Solutions

Achieving stormwater performance targets involves change, both at the land use level, and atthe site design level.

Initiating change in stormwater management through land use or site design may involve twotools of local government: the Official Community Plan (OCP) and the Liquid WasteManagement Plan (LWMP), and their related bylaw tools.

Official Community Plans tend to be led by planners, with input from engineers oninfrastructure sections. Liquid Waste Management Plans tend to be led by engineers, withlittle or no input from planners. Both processes involve approval by a Local Council or aRegional Board.

Official Community Plans (OCPs)Official Community Plans are statements of broad objective and policy to manage land useand growth in municipalities or in designated areas of regional districts. While these plansmust designate land uses, they also may address social, environmental and sustainabilityissues at a broad level.

Related tools are Regional Growth Strategies, Neighbourhood Plans, Zoning Bylaws,Subdivision Bylaws and Development Permits, among others. While these tools are notcentered on stormwater management, the provincial Local Government Act has expresslypermitted local governments to use these tools to manage environmental impacts, runoff andimpervious area.

Liquid Waste Management Plans (LWMPs)Creating change in stormwater practices also may be triggered by a Liquid WasteManagement Plan (LWMP). A Liquid Waste Management Plan charts a local government’sproposed future course of action with respect to the management, collection, treatment anddisposal of the sewage, stormwater and other wastewater effluents.

LWMPs are voluntary, and are created by local governments under a public process in co-operation with the Province. There are currently about 40 LWMPs adopted or in process inBC. Although the emphasis of most LWMPs has to date been on sanitary sewage, there willbe an increasing emphasis on non-point-source pollution and stormwater in new LWMPs, oras existing LWMPs are updated or amended.

Case Study ApplicationsThis chapter presents two case study applications that have developed content for theGuidebook:

� Suburban Municipality – the City of Chilliwack

� Rural Regional District – the Regional District of Nanaimo

These case studies have provided an opportunity to test and refine core concepts contained inthis Guidebook with respect to integrating stormwater management with land use planning.


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Integrating Stormwater and Land Use StrategiesOfficial Community Plans and Liquid Waste Management Plans, although often produced inisolation, are actually highly related exercises, as shown below:

Official Community Plan (OCP) Liquid Waste Management Plan (LWMP)

Sets land use designations Deals with sanitary sewage and stormwaterconsequences of land use designations

Adopted by Council/Board bylaw Adopted by Council/Board bylaw

Involves public process Involves public process

Updated periodically Updated periodically

Planner-led Engineer-led

Rather than view these as separate processes, it is useful to recognize the complementary anditerative nature of these two tools, as illustrated in Figure 4-1. Changes in land use policycreate changes in liquid waste policy, and ecological or financial limitations on liquid wastesystems may limit land use change.

Each local government will have a different Official Community Plan, Liquid WasteManagement Plan, and other bylaws. As almost every bylaw comes up for reviewperiodically, changing stormwater management policies is an opportunistic process; changewill be made when the opportunity exists to make change.

Figure 4-1


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4.2 Liquid Waste Management PlansThe provincial Waste Management Act allows a municipality or regional district to developan LWMP for approval by the Minister of Water, Land and Air Protection. The Minister canalso order a local government to develop or revise an LWMP.

When the Guidelines for developing an LWMP were first published in 1992, urbanstormwater runoff was included because the Ministry considered stormwater to be a resourceto be protected. The 1992 Guidelines outlined a 3-stage process for developing an LWMP,and listed the various waste streams to be addressed, including non-point source pollution instormwater runoff. The three stages are:

� Stage 1 - Identify Options� Stage 2 - Evaluate Options� Stage 3 – Prepare and Adopt Plan

Public participation is an integral component of each stage. This requirement provides anopportunity for a feedback loop that should also help broaden community support for therelated but separate ISMP process for the stormwater component of an LWMP. Amethodology to involve stakeholders in ISMP development is explained in Part C.

The Minister must be satisfied that there has been adequate public review and consultationwith respect to the development, amendment and final content of the LWMP beforeproviding sign-off. When approved, the LWMP authorizes disposal or re-use of municipalliquid waste. The local government then has the authority to spend the allocated public fundson the identified works and projects contained within the plan. Ideally, the LWMP shoulduse a 20 to 40-year planning horizon.

The 1998 NPS Action Plan, introduced in Chapter 1, also identifies an LWMP as a tool todeal with pollution from stormwater runoff.

Stormwater Management Role of Regional DistrictsTo the date of writing, stormwater management in British Columbia has been focused onmunicipalities, not regional districts. The only regional districts that are highly active instormwater management are the Greater Vancouver Regional District (GVRD) and theCapital Regional District (CRD). Within these two relatively urbanized regional districts,most of the land area falls within municipal boundaries. Therefore in the GVRD and theCRD, the regional district role is as a coordinator and economy of scale service provider, withthe primary stormwater management role being provided by the member municipalities.

Outside of these two metropolitan regions and other municipalities, the great majority of theland area in British Columbia is administered as electoral areas within regional districts.Stormwater management in these relatively rural regional districts has been limited to date.In many cases, there is little active stormwater planning, other than that provided for drainageof roads administered by the provincial Ministry of Transportation and Highways.


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Relationship between LWMP and ISMP ProcessesThere are two ways that the LWMP process potentially dovetails with stormwatermanagement planning:

� Regional Scale – This is a macro view where a comprehensive approach isadopted; ISMPs are also part of the stormwater component of an overall LWMP.

� Watershed Scale – This is a micro view where the ISMP itself becomes thestormwater component of the LWMP; the ISMP delves into watershed-specificdetails

ISMP Technical ProductsLooking ahead to Part C, an ISMP comprises three core technical products:

� ISMP Technical Product 1 - Inventories of the physical and biological systems

� ISMP Technical Product 2 - Component plans to protect the resources, resolveidentified problems and accommodate land development and growth

� ISMP Technical Product 3 - An implementation program comprised of sixelements:

� Administration

� Projects, Phasing and Budgets

� Financing Mechanism

� Community Education

� Maintenance

� Performance Monitoring

These three technical products generally parallel the three LWMP stages. The distribution ofeffort among the three products should be balanced. Often effort is concentrated on theinventory phase, and not enough effort is invested in the elements of an implementationprogram. The best plan, without a sound implementation strategy, can result in watershedconditions getting worse with time rather than better.

Input to Stormwater Component of Stage 1 LWMPThis is the stage where background information is gathered and the various options forresolving problems are explored. This includes identification of at-risk drainage catchments(refer to Chapter 4). The ISMP Technical Product 1 would be undertaken at this stage.

Input to Stormwater Component of Stage 2 LWMPThis is the stage at which a guiding philosophy for stormwater management is crystallized,policies are adopted and commitments are made to achieving performance targets (refer toChapter 5) through integration with land use planning. Section 4.4 presents the elements of apolicy framework to achieve integration.

This is also the stage at which options and/or approaches to stormwater management arestudied in more detail in terms of cost and feasibility. This evaluation process should resultin a final (one or two) best option(s) to advance to Stage 3. In short, ISMP Technical Product2 could be a Draft Stormwater Plan within the overall LWMP.

Input to Stormwater Component of Stage 3 LWMPThis is the stage at which the stormwater component, as well as the overall LWMP itself, isfinalized and adopted. The main focus is on developing an adaptive program that will enablelocal government to move from planning to action in an affordable manner (refer to Part C).


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4.3 Relationship Between OCPs and LWMPsThere is a clear link between land use planning required of local governments in the LocalGovernment Act (sections 944, 945) and waste management planning described in the WasteManagement Act (part 1, section 16).

An OCP provides a clear statement to the public and the province about a local government’sgrowth management objectives and provides the rationale for subsequent land useregulations.

An OCP Provides the Foundation for an LWMPIn most cases where OCPs are in place, the local government planning statement (bylaw) willform the basis of waste management plans. The purpose of an LWMP is to minimize theadverse environmental impact of the OCP and to ensure that development is consistent withMinistry of Water, Land and Air Protection objectives.

Local government land use planning is essentially a process of anticipating changes in landuse and determining how to manage or influence these changes for the benefit of thecommunity or region. In OCPs, local governments attempt to:

� Identify rural and urban development areas� Assess the suitability of different areas for development� Identify the expected sequence of urban and rural land development, including

the proposed timing, location and phasing of sanitary and stormwaterinfrastructure

Where OCPs have been completed and adopted by bylaw, they should be used as afoundation for an LWMP.

LWMPs should be incorporated in total or in part as a schedule to an OCP. This will help toprevent land use decisions that eliminate or pre-empt future options for environmentalmanagement.

Take Whatever Step Comes FirstIn some cases, an LWMP process may be a trigger that focuses attention on stormwatermanagement. Public concern related to flooding or habitat loss may be the trigger.Alternatively, an OCP public process may communicate public interest in raising localenvironmental and habitat protection standards.

Whatever the initial driver, at the end of the process a local government’s OfficialCommunity Plan should include goals and objectives for stormwater management. Thesegoals and objectives, or a variant of them, might first reside in a LWMP, and then be adaptedto the OCP in the next review process. Or they may originate in the OCP process, and thenbe detailed through an LWMP. Either way is entirely acceptable.

The stormwater goals and objectives should be integrated into land use and growthmanagement decisions that are embodied in the Official Community Plan, Regional GrowthManagement Strategy, and other local government bylaws.

The Link Between Land Development and Stream ProtectionLocal governments may consider directing growth away from sensitive areas, or zoning forland use that is compatible with stream protection. However, it is recognized that land usedecisions are based on a broad range of considerations, among which stormwater is only onefactor.

Where pre-existing land uses, or new designations, potentially impact sensitive watercourses,there will be a need to manage the development or re-development to meet a localgovernment’s goals and objectives for environmental protection and restoration.

The key to making land development compatible with stream protection is to applyappropriate stormwater source control strategies to reduce runoff volume and rate, asdiscussed in Chapter 7.


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4.4 Stormwater Management Goals, Objectives andPolicies

As discussed in Part A of the Guidebook, stormwater management and land use need to beintegrated to address the source of stormwater-related problems. A critical step is to mergeappropriate stormwater management goals, objectives and policies into a local government’sOCP.

OCPs, and related Neighbourhood Plans, commonly set out broad goals, objectives andpolicies that guide implementation actions by local governments. Although OCPs do notbind a local government to a specific action, they prohibit the local government from actingcontrary to the stated policies.

Establishing the right stormwater management policy framework and merging thisframework with the OCP will ensure that land development decisions (at the planning andsite design levels) address stormwater management objectives.

Case Study Example: Customizing a FrameworkThe City of Chilliwack’s Policy and Design Criteria Manual for Surface Water Management(2002) includes stormwater management goals, objectives and policies that were developedthrough an inter-departmental and inter-agency process, which involved:

� City staff from both planning and engineering departments

� Representatives of senior government agencies (federal fisheries, provincialenvironment and agriculture ministries)

This process consisted of five working sessions where the core concepts of this Guidebookwere presented to City staff and agency representatives. To provide context and relevance forparticipants, and to test the Guidebook concepts, local development projects were used ascase study applications.

Outcome of Working SessionsThese sessions created a broad understanding of integrated stormwater management, whichwas the key to agreeing on:

� A stormwater management goal and a set of five related objectives

� A set of supporting policy statements to translate the goal and the objectives intoaction at three scales: the watershed, the neighbourhood and the site

The over-arching philosophy of the policy framework is that stormwater management andland use planning must be fully integrated to ensure complete solutions to stormwater-relatedproblems.

This over-arching philosophy was endorsed through a series of working sessions withstakeholder focus groups, including:

� The Development Process Advisory Committee (representing the developmentcommunity)

� The Agricultural Commission (representing the agricultural community)

� A Public Forum (representing the broader community)

Chilliwack’s resulting stormwater management goals, objectives and policies are presentedon the following pages. The detailed wording was refined through an iterative and interactiveprocess with City staff and agency representatives.

Customizing Policies for the Local SituationThe goals, objectives and policies established through the Chilliwack process provide anexample of what an appropriate policy framework could look like. However, each localgovernment should adopt policies that reflect their individual situation, and that also reflect along-term vision that is shared by all stakeholders (as discussed in Chapter 10).


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These goals and objectives reflect the need for flexibility to account for variability in localconditions, and emphasize the importance of demonstration projects to prove theeffectiveness of new approaches.

Each of these stormwater management objectives is supported by a set of policies. These arepresented on the following pages.

Stormwater Management Goal(for all watersheds in Chilliwack)

Implement integrated stormwater management that maintains or restores the WaterBalance and water quality characteristics of a healthy watershed, manages flooding andgeotechnical risks to protect life and property, and improves fish habitat values overtime.

Stormwater Management Objectives1. To manage development to maintain stormwater characteristics that emulate the pre-development natural watershed.

2. To predict the cumulative stormwater impacts of development and to integrate thisinformation with other economic, land use and sustainability objectives and policieswhen considering land use change.

3. To regulate watershed-specific performance targets for rainfall capture, runoffcontrol, and flood risk management during development, and to refine these targetsover time through an adaptive management program.

4. To identify, by example and pilot studies, means of meeting the performance targetsby application of best management practices, and to remove barriers to use of thesepractices.

5. To support innovation that leads to affordable, practical stormwater solutions and toincreased awareness and application of these solutions.


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Stormwater Management Objective #1

To manage development to maintain stormwater characteristics thatemulate the pre-development natural watershed.

Supporting DiscussionStreams that are stable in their natural condition tend to become unstable after unmitigatedurban development in the watershed, and become subject to instream erosion andsedimentation which impacts both flood risk and fish habitat.

These risks are often most pronounced in small catchments, which tend to be first orderstreams. This is because land use change may cause a high percentage change inimpervious area in proportion to the size of a small catchment. This change results in alarge change to flows in the stream, creating an unstable condition.

To avoid these impacts, it is necessary to mimic the characteristics of the pre-developmenthydrograph, including total flow volume, peak flows and hydrograph shape. Reaching thisobjective requires an integrated stormwater strategy that includes rainfall capture to reducestormwater volume.

Changes in stream flow due to urbanization have greater impacts than changes in waterquality, however, many of the best management practices (BMPs) that will provide rainfallcapture and detention will also contribute to maintaining water quality.

Supporting Policies1. Integrated stormwater management planning (ISMP) processes shall be undertaken

to develop integrated master drainage plans (MDPs), first for the Chilliwack CreekWatershed, followed by the Hope River Watershed, and then the Sumas/CollinsonWatershed.

2. Each master drainage plan shall develop a practical and affordable action plan forminimizing runoff volume, reducing both the rates and duration of peak flows, andsustaining baseflows.

3. Each action plan will integrate a practical and affordable strategy for protecting and/orimproving water quality, and minimizing non-point sources of sediment and pollutantloading.

4. Within each watershed planning process, priority effort shall be focused in at-riskcatchments, defined based on the risks of land use change in relation to the fisheriesvalues and potential for flooding within the catchments.

5. For designated at-risk catchments, the City shall set stormwater performance targetsand site design criteria based on site-specific rainfall and soils data.

6. Each master drainage plan shall include an adaptive management program to testand refine the stormwater performance targets and site design criteria over time,based on more detailed data collection, modeling, monitoring and analysis.


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To predict the cumulative stormwater impacts of development and tointegrate this information with other economic, land use and

sustainability objectives and policies when considering land usechange.

Supporting DiscussionThe stormwater impacts of land use change are incremental and cumulative. Land usedecisions must be made with full awareness of both the incremental impacts of individualdevelopment projects and the cumulative impacts of building out existing zoning.

The guiding principles for integrated stormwater management should influence the details ofland use and site planning.

Stormwater is one of many factors to be considered in land use decisions, but stormwaterobjectives will often be compatible with other development objectives.

Supporting Policies1. When considering changes to its OCP or zoning bylaws, the City shall assess the

cumulative impact of proposed development on stormwater flows and fish habitat and thepotential for mitigation of these impacts through establishment of performance targetsand application of best management practices.

2. The City will consider use of density bonus provisions to encourage more green space fordevelopments in designated at-risk catchments.

3. For areas where the City has not yet established stormwater performance targets,applications for significant changes to OCP land use designations or zoning shall berequired to include a stormwater management strategy with:

(a) a statement of cumulative impacts of stormwater on the receiving watershed and sub-catchment

(b) application of science-based performance targets for rainfall capture, runoff control and flood risk management


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To regulate catchment-specific performance targets for rainfallcapture, runoff control, flood risk management, and water quality

protection during development, and to refine these targets over timethrough an adaptive management program.

Supporting DiscussionChapter 5 provides background information on the need for, role and basis for performancetargets, and shows how to:

(a) set preliminary performance targets for rainfall capture, runoff control, flood riskmanagement

(b) set up an adaptive management program for improving these preliminarytargets over time.

Performance targets should be customized to each drainage catchment because theconditions, constraints, problems and opportunities will vary from one catchment to another(e.g. different rainfall characteristics, pattern of streams and lakes, drainage infrastructure,soil characteristics and development patterns). Appropriate strategies for meeting rainfallcapture and runoff control targets will depend on local conditions, as illustrated by thefollowing examples:

Example 1: Where there are few constraints to infiltration, and little space forcommunity detention, both rainfall capture and runoff control may be handled bysmall-scale storage and infiltration systems on individual development parcels.

Example 2: Where infiltration opportunities are limited, more rainfall capture maybe achieved by water re-use combined with some on-site infiltration. Runoff controlwould be then provided by community detention facilities, rather than on-parcel.

(Chapter 7 provides guidance for selecting stormwater source control practices are mostappropriate for different land use types, soil conditions and rainfall characteristics).

Supporting Policies1. Rainfall capture facilities that meet the rainfall capture performance targets must be

provided for all new developments in designated catchments. Preference shall be givento water re-use and/or infiltration systems, backed up by small-scale storage facilities asrequired to support the re-use or infiltration rate of the site soils, where feasible.

2. Where site infiltration rates allow, runoff control performance targets may be met byincreasing the storage capacity of rainfall capture facilities. In cases where on-site soilsare not suitable, constructed wetlands (for drainage areas over 10 acres) or detentionponds (for smaller drainage areas) shall be provided to meet the runoff controlperformance targets.

3. In cases of new development, adequate conveyance routes for major storms shall beprovided to meet the flood risk management performance targets.

4. For each designated catchment, as affordable, the hydrologic and water qualityperformance of representative rainfall capture and runoff control facilities shall bemonitored, and the performance targets shall be adjusted for future development basedon the monitoring results.

5. For each designated catchment, as affordable, early warning indicators shall bemonitored to determine how well site level actions are maintaining or restoring a healthycatchment.


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To identify, through demonstration projects, means of meeting theperformance targets by application of best management practices, and

to remove barriers to use of these practices.

Supporting DiscussionThe performance targets are intended to set minimum requirements, while allowing flexibilityfor applicants to be innovative and cost-effective in meeting the target.

The flexibility of this approach will be attractive for projects with sophisticated design teams.

However, during the learning curve associated with the performance standards, and for smallprojects, or those that do not normally involve a design team (e.g. a single family dwelling),there is a need for a set of examples that show how the performance targets can be met in apractical and affordable way.

Supporting Policies1. The City will devise and maintain a manual of best management practices that illustrate

how performance targets may be achieved.

2. Local demonstration projects will be encouraged on City land and private land to increasepublic and developer understanding of the best management practices, and to test theirperformance.

3. The City will review its existing bylaws to identify and remove clauses that would act as abarrier to the proposed best management practices. Refer to Part A for more detail.


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To support innovation that leads to affordable, practical stormwatersolutions and to increased awareness and application of these

solutions.

Supporting DiscussionNew best management practices, and variations to existing practices, are constantly beingdeveloped. There is a need for a system that can adapt to this constant change.

There will also be a need for technical training of staff and the development community.This training will need to be updated and repeated to reflect new information and newparticipants.

Supporting Policies1. Applicants shall be encouraged to propose alternative solutions to meet the

performance targets, subject to the approval of City staff.

2. Educational events and training media shall be supported in co-operation with seniorgovernments and other local governments.


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4.5 Policy Transition in a Rural Regional District

Case Study Example: A Five-Year Stormwater Management ProgramThe Regional District of Nanaimo is entering a transition from having no role in stormwatermanagement to playing a more active role, by creating a five-year Stormwater Action Plan.

This case study illustrates how a rural regional district is making the policy transition to suchan active role.

Enhancing the Stormwater Component of an LWMPThe Regional District of Nanaimo (RDN) created a voluntary LWMP in 1997. The focus ofthe Plan was on wastewater treatment. The Plan was approved by the (then) Minister ofEnvironment, Lands and Parks.

With the written encouragement of the Minister, the RDN proceeded to upgrade thestormwater management components of its Phase 3 LWMP in 2001.

To accomplish this task, the RDN partnered with the (current) Ministry of Water, Land andAir Protection and the Georgia Basin Ecosystem Initiative to develop a five-year StormwaterAction Plan.

The Need for Stormwater Management in Rural Regional DistrictsTo date the emphasis of stormwater planning in the RDN has been within the membermunicipalities of Nanaimo, Parksville and Qualicum Beach. While most of the RDN isresource land in forestry uses, there are extensive areas at lower elevations in the electoralareas that are developed. This development has created changes in stormwater flows andwater quality, when compared to natural forested watersheds. Common changes resulting inaltered flows and water quality are listed in Table 4-1.

Many of the land use changes identified in Table 4-1 do not create significant stormwaterproblems if the amount of change is small. However, the impacts are cumulative; as moreland use change and densification occurs, stormwater impacts become more significant ifthey are not mitigated.

Table 4-1: Land Use Changes with Potentialto Affect Stormwater Quantity and Quality

Agricultureand Acreage

Single andMulti FamilyResidential

Industrial,Commercial

andInstitutional

Removal of forest cover X X X

Installation of open ditches or underdrainage X X X

Removal of seasonal or permanent wetlands X X X

Soil erosion during construction X X X

Soil erosion from fields (if winter cover cropsare not used)

X

Introduction of chemical nutrients andpesticides

X X X

Application of manure X

Removal or compaction of absorbent soils inlandscape areas

X X

Paving of roads, streets, driveways, parkingand yard areas and patios

X X X

Roof area drainage X X X

Introduction of chemical pollutants, either asnon-point-source runoff, or as point sourcepollution such as spills, accidents, andoutflows

X X X


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Stormwater Role for RDNThe RDN had a variety of reasons for deciding to take on a more active stormwater planningrole, including:

1. Stormwater impacts will increase unless mitigated.

As land development in the electoral areas increases, stormwater impacts and relatedrisks of flooding, property damage and degradation of aquatic ecosystems will increase.

2. Fish, shellfish and clean water are a part of the RDN’s heritageand economic resources.

The RDN is bestowed with many productive salmon bearing streams and shellfishbeaches. The lifestyle of its residents and the reputation of the region are enriched bythese resources. Managing stormwater is a part of maintaining quality of life andattractiveness as a place for tourists and new residents.

3. Stormwater planning in electoral areas is not being done.

In many cases, stormwater planning can not be done efficiently for individualdevelopments, since both the stormwater impacts and solutions involve large areasoutside an individual site. Stormwater planning by the RDN can provide economy ofscale. In addition, there is no other agency that provides watershed-scale stormwaterplanning in electoral areas. The stormwater activities of the provincial Ministry ofTransportation and Highways are limited to drainage associated with roadways.

4. Many stormwater impacts can be avoided.

With proper stormwater planning and land development practices, mitigation of manystormwater impacts can be achieved. Since the RDN manages land use (other thanagriculture and forestry), it has better tools than other agencies to address stormwaterplanning associated with land use development.

5. Stormwater planning now can avoid future public expense.

Unmanaged stormwater often leads, eventually, to major public expense in infrastructureto solve flooding or erosion problems, sometimes driven by litigation. Planning aheadcan find less expensive solutions, minimize public expense by solving stormwaterproblems at the source – the development - and provide for financial mechanisms tofund stormwater infrastructure where it is necessary.

6. Stormwater flows across jurisdictions and land uses.

There are several cases in BC where successful litigation has been brought by farmerswith flooded fields due to unmitigated upstream urban development. And there arecases like Walkerton, Ontario, where farm drainage has had a drastic impact on drinkingwater supply and human health. As municipalities in the Regional District of Nanaimoundertake stormwater management and drinking water projects, there is both anopportunity and a need for the RDN to plan co-operatively, especially where watershedscross jurisdictional boundaries.

The promise of stormwater planning is that mitigation of many stormwater impacts can beachieved by management of the way that land is developed.


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Focusing Rural Stormwater Planning EffortsThe proposed RDN Stormwater Action Plan will focus on stormwater education and co-ordination throughout the region, and stormwater planning in electoral areas. Emphasis willbe on managing urban development to mitigate stormwater quantity problems, and onmanaging related non-point source pollution.

The need for stormwater management will vary within different areas of the RDN. Forexample, areas of the region that are not yet developed will not have urban stormwaterconcerns, and timber harvesting areas of the region are administered by the Province.

Two Levels of EffortThe RDN stormwater management program will have two levels of effort:

� Integrated Stormwater Management for At-Risk Catchments:

The focus of stormwater management in the RDN will tend to be rapidly developingareas. A pilot study has identified at-risk drainage catchments (catchments whereconditions combine existing and/or pending urban development with high risks of eitherdrainage problems and/or environmental impacts). These at-risk catchments will be anopportunity for the RDN to test integrated stormwater management approaches.

Integrated stormwater management means planning that recognizes the relationshipsbetween land use planning, stormwater quantity and quality, and environmental factors,creating a plan that balances all three for optimum results.

It is possible that stormwater solutions in at-risk drainage catchments will requireinvestment in public stormwater facilities.

� Basic Stormwater Management for Other Developments andAgricultural Areas:

Outside of the at-risk catchments that require intensive planning, the RDN will take aproactive approach to basic stormwater management throughout its jurisdiction to avoidfuture public costs due to cumulative impacts of development. Basic stormwater BMPsand performance targets will be applied in all land uses and densities.

For example:

� Poorly designed developments may create unnecessary increases in runoff,resulting in flooding and downstream impacts and creating new at-risk drainagecatchments over time with resulting taxpayer expense.

� Water quality issues, like lack of erosion control during the construction period,are issues throughout the RDN.

� Agricultural areas of the RDN may also have a need for basic stormwatermanagement. Although agricultural areas are generally administered by theProvince, there are potential stormwater impacts from agricultural drainage ondownstream urban or fishery areas. Unmitigated urban development can alsohave dramatic flooding impacts on downstream agriculture.

The basic stormwater management program will create public education programs, aswell as broadly applicable regulations that will influence the way that private land isdeveloped, with the intent to minimize the need for public investment in stormwaterfacilities.

Management ArrangementsManagement arrangements in the RDN’s stormwater management program include:

� Management of potential pollutants near drinking water sources should be thesubject of a separate program.

� Regulation of forestry and agricultural practices is under the jurisdiction of theProvince of British Columbia. The RDN will be cognizant of resource andstormwater planning by related Provincial agencies.

� The RDN will co-operate with its member municipalities to offer economy ofscale in provision of stormwater information, and will support joint planningwhen stormwater issues cross electoral area or municipal boundaries.

� Drainage catchments that may already be impacted as the result of existingdevelopment may be the subject of stewardship and restoration efforts, often inco-operation with non-government organizations.


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An Action Plan for the Transition to Stormwater ManagementThe RDN has opted for a gradual entry into an active stormwater management role. It willtake several years to increase public awareness of stormwater issues and solutions and todetermine an appropriate role and funding mechanism for stormwater management on landswithin its jurisdiction.

While being methodical about entering stormwater management, it is also important that theRDN put stormwater management tools in place as soon as possible, so that further landdevelopment without stormwater mitigation does not occur at a large scale.

A five-year Stormwater Action Plan is proposed to allow the RDN to carefully plan its role instormwater management. Table 4-2 provides an outline of the Plan.

Each Year will have a FocusImplementing the Action Plan will be subject to approval of general stormwater programfunding. Once started, each year in the Stormwater Action Plan has a focus:

Year One Focus: Getting Started

Year Two Focus: Revise Infrastructure Standards

Year Three Focus: Develop Training and Public Awareness Programs

Year Four Focus: Implement Actions

Year Five Focus: Review and Adjust Action Plan

The Action Plan allows for effective public consultation, outreach and training for thedevelopment community, demonstration projects, incentives, and co-operation with otherlevels of government and the private sector.

Regulatory ChangeCareful consideration will be given to regulatory change – first, to remove barriers in existingregulations to better stormwater management, and second, to consider to what extent existingregulations should be refined (e.g. zoning and subdivision bylaws).

It is also envisioned that stormwater issues and policies would be considered as each OfficialCommunity Plan undergoes a regular review.

Transfer of Approval Powers from the Ministry of Transportation and HighwaysThe potential transfer of subdivision approval powers from the provincial Ministry ofTransportation and Highways to rural regional districts may also provide a trigger forimplementing stormwater management in the RDN. In the meantime, the Ministry is open toencouraging better stormwater performance in development applications, provided that theapproach does not increase the costs to the Province of BC.

Updating of Action PlanAdopting the Action Plan does not commit the Region to ongoing funding mechanisms.These will be considered as a part of the Action Plan process, with the intent that the RDNdesigns a practical and affordable system to address stormwater issues.

At the end of the five-year Action Plan, the RDN will have developed a clear understandingof appropriate stormwater management approaches that are customized to the localenvironment and acceptable to the development community.

It is envisioned that in the fifth year of the Action Plan, a new plan will be created for thefollowing five year period or longer, based on the needs, opportunities and priorities that areapparent at the time. The Stormwater Action Plan is intended to be updated every five yearsas the program moves ahead.


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Table 4-2: Regional District of Nanaimo Stormwater Action Plan

Priority Projects Lead Role RDNBudget

Potential AdditionalFunding

1 YEAR ONE FOCUS: GETTING STARTEDAdopt the Stormwater Action Plan

Create introductory information and public outreach materials

Identify priorities and budget for RDN stormwater management planning in at-risk drainage basins, in consultation with member municipalities

Design and adopt stormwater funding and administrative mechanisms (e.g. region-wide service area for research, coordination, planning and public awareness;specific local service areas for capital and operating projects as required)

2 YEAR TWO FOCUS: REVISE INFRASTRUCTURE STANDARDSParticipate with others (e.g. member municipalities) to create technical information materials on low impact stormwater standards and BMPs – print / web / video

Review existing bylaws and remove barriers to low impact standards and BMPs for better stormwater management

3 YEAR THREE FOCUS: DEVELOP TRANING AND PUBLIC AWARENESS PROGRAMSIn partnership with member municipalities, train staff, developers, builders, NGOs and the public on low impact stormwater standards and BMPs

Consider need for, and design draft stormwater clauses including performance targets and example details as potential amendments to RDN bylaws in co-operationwith appropriate provincial and federal agencies

Consider stormwater impacts as a factor in regular Official Community Plan or zoning reviews and amendments

4 YEAR FOUR FOCUS: IMPLEMENT ACTIONSIf applicable, amend bylaws to include new stormwater clauses

In co-operation with member municipalities, senior governments and the private sector, complete demonstration BMP installation projects

For an at-risk watershed, complete an Integrated Stormwater Management Plan as a pilot project towards the creation of a stormwater local service area

5 YEAR FIVE FOCUS: REVIEW & ADJUST ACTION PLANIf appropriate, proceed to implement stormwater local service area

Create an awards program that recognizes excellence in stormwater management

Review the status and success of the Action Plan

Prepare an updated five-year Action Plan


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Administering the RDN Stormwater Management ProgramThe RDN is considering the funding of stormwater management at three levels:

Level One - Stormwater Public Facility Construction andMaintenance for at-risk catchments could be funded by a local service area approach.This would fund the capital and operating costs of public facilities related to the benefitingtaxpayers. A local service area is established by a bylaw that describes the service, identifiesthe boundaries of the service area along with the municipalities and electoral areas thatinclude participating areas, and sets out the costs and means of cost recovery for the service.If the local service area requires borrowing, the bylaw must receive the approval of affectedvoters.

Level Two - Basic Stormwater Planning and Public Awareness for theentire RDN would be funded through a region-wide service area or a stormwater utility. Arelatively low investment per taxpayer could provide funding for the shared aspects of basicstormwater management. Shared aspects could include dissemination of public information,monitoring of risks, stormwater research and planning and regulation.

The basic stormwater management funding program may include identification of integratedstormwater planning for at-risk drainage catchments. By having this planning fundingprovided by the region-wide service area, sufficient information will be available for voters toconsider specific capital and maintenance works to be funded through specific local servicearea initiatives.

Subject to legal review, a region-wide service area for stormwater management may beestablished through either the LWMP process or by the assent of the electors by either vote orcounter petition opportunity.

As an option, a stormwater utility could also fund stormwater planning, works and servicesby fees and charges established under S. 363 of the Local Government Act. The Board maybase the fee or charge on any factor specified in the bylaw, including by establishing differentrates or levels of fees in relation to different factors such as parcel imperviousness.

Level Three - Regulation of Land Development provides a third form offunding for stormwater management. It is standard practice that rezoning or subdivisionapplications above a certain minimum size are required to provide stormwater works andservices, since mitigation of stormwater impacts is a legitimate cost of development. Thissource of funding works well for larger, new developments, especially in greenfieldsituations.

Stormwater improvements may be paid for directly by the developer, or may be funded bydevelopment cost charges which pool funds for public projects that are made necessary by thedevelopment. The requirements for this type of developer-funded stormwater planning andstormwater works should be included in regional district bylaws.

Requirements may be added to regional district bylaws and administered in tandem with theProvincial Approving Officer of the Ministry of Transportation and Highways, or could beapplied directly by the regional district if the subdivision approving function were held at theregional district level. However, in cases where substantial development or developmentapprovals already exist, and the new development is small-scale densification or infill, therewill be a need for stormwater planning to be funded by the regional district.

Partnerships for the RDN Stormwater Management ProgramThere are several agencies that could partner with the Regional District of Nanaimo tosupport implementation of the basic stormwater planning program:

� Member municipalities, for economy of scale in producing public outreach and technicalinformation materials

� The provincial Ministry of Community, Aboriginal and Women’s Services, throughplanning grants for planning and bylaw changes

� The Canada-BC Infrastructure Program, for design and capital assistance

� The Georgia Basin Ecosystem Initiative, for ongoing support of pilot and implementationprograms

� The Federation of Canadian Municipalities Green Municipal Enabling Fund and relatedfunds

Chapter Five

5.1 Knowledge-Based Approach� Overview

5.2 At-Risk Methodology� Integration of Knowledge� Identification of Priorities� Introduction to the Interdisciplinary Roundtable Process� Timely Decision Making� Focused Working Sessions

5.3 Case Study: Stormwater Priorities in the Regional District of Nanaimo� Watersheds in the RDN� Workshop Structure and Methodology� Land Use Workshop� Drainage and Aquatic Habitat Workshop� Reporting Results and Follow-Up Questionnaire� Strengths and Limitations of the At-Risk Methodology� Building Support Through the Interdisciplinary Roundtable Process

5.4 The Role of Mapping� Keeping it Simple� Graphic Overlay versus Geographic Information System

Setting Priorities for Early Action



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5.1 Knowledge-Based ApproachStormwater management may be driven by expressed goals, objectives and policies asoutlined in Chapter 4, or it may be driven by evolving crises on the ground, or both. In eithercase, a key step for any municipality or regional district undertaking a stormwater planningprocess is to set priorities for action.Setting priorities for action should be at two scales:

� At the regional scale – deciding which watersheds are priorities

� At the watershed scale – deciding which tributary drainage catchmentsto focus on within priority watersheds

OverviewThis chapter presents a methodology for prioritizing action that focuses on low-cost results bygetting the right people together in working sessions. This ‘knowledge-based’ approachcontrasts with one that starts with extensive raw data collection and sophisticated mapping.

If the right people with the right knowledge are involved at the start, a knowledge-basedapproach will be both time-efficient and cost-effective. This combination should translateinto cost savings that can be applied to stormwater solutions in the field.

There are many approaches to setting priorities, ranging from data-collection-intensive toknowledge-based. In regions where some watershed areas are at high risk, and others maynot yet be priorities, the use of a knowledge-based approach to distinguish those catchmentsrequiring early intervention can be an efficient way to initiate action where it is needed themost to avoid or mitigate stormwater threats.

As stormwater management actions are implemented, more rigorous long-term datacollection through a monitoring program is appropriate to allow adaptive management ofstormwater solutions.

5.2 At-Risk MethodologyThe At-Risk Methodology (ARM) creates an early focus on areas that may need priorityattention to avoid pending stormwater impacts.

Priority action should be focused in at-risk drainage catchments where there is both highpressure for land use change and a driver for action. The latter can be either:

� a high-value ecological resource that is threatened, or� an unacceptable drainage problem

It is important to focus on areas of land use change because this is where problems can beturned into opportunities. Land use change is the root cause of stormwater’s ecological andproperty impacts, and this root cause can be eliminated through land development practicesthat reduce the volume and rate of runoff at the source. Local governments also usually havejurisdiction over, and focus their attention on, areas experiencing land use change.

Integration of KnowledgeIn order to identify at-risk drainage catchments it is important to integrate knowledge fromeach of the planning, ecology and engineering disciplines:

� Planning – to identify where the areas are with high pressure for land use change

� Ecology – to identify where there are significant aquatic resources.

� Engineering – to identify where there are chronic drainage problems

The integration of this information through discussion and brainstorming in aninterdisciplinary roundtable process will enable the identification of at-risk drainagecatchments – those where future land use change threatens to degrade high-value resources orexacerbate drainage problems.


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Identification of PrioritiesThe result of the foregoing process will be identification of priority drainage catchment areasfor stormwater planning and action. The top priority drainage catchment is particularlysignificant because of its potential to act as a demonstration project for remaining watershedsto demonstrate how:

� profitable land use can proceed while preventing stormwater-related problems

� land development practices that reduce runoff at the source can protect aquatichabitat and property from stormwater related impacts

By monitoring the performance of demonstration projects, land development and stormwatermanagement practices can be improved over time for remaining watersheds.

Introduction to the Interdisciplinary Roundtable ProcessThe most effective and affordable way to identify at-risk watersheds for priority action is totap the knowledge of people within any regional district or municipality who have thenecessary planning, ecology and engineering knowledge. This can be accomplished throughan interdisciplinary roundtable process that integrates planning, engineering, and ecologicalperspectives from the very beginning of a stormwater planning process.

The inputs and outcomes that define the interdisciplinary roundtable process areconceptualized in Figure 5-1. The knowledge-based mapping products from three focusedworking sessions (land use, ecology and engineering) feed into an interdisciplinaryroundtable. This roundtable is where representatives from the three focused working sessionsoverlay key information on future land use, aquatic resources and drainage problems toidentify at-risk drainage catchments and prioritize action.

The interdisciplinary roundtable is especially appropriate for a jurisdiction that has multiplewatersheds. It need not be, and should not be, a lengthy process, especially if the goal is toachieve early action. The objective is to make initial decisions based on informed judgement.

Figure 5-1


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Timely Decision MakingKey decisions can be made in a relatively short period of time if:

� The working session is focused on achieving a specific desiredoutcome –

For example, the desired outcome could be the selection of a top priority at-risk drainagecatchment to focus early action. Once action is implemented, this catchment willbecome a demonstration project for remaining watersheds. A secondary desiredoutcome would be to identify the next 5 to 10 (say) priority watersheds to provideguidance for the longer-term stormwater management program.

� The information that is key to achieving the desired outcome ispresented -

The focused working sessions should produce overall maps of the stormwater planningregion, highlighting the areas where:

� there is the greatest pressure for land use change� ecological resources are concentrated or threatened� chronic drainage problems (i.e. ‘hot spots’) occur

The overlay of this information allows an assessment of drainage catchment risk, whichprovides a focal point for action.

The focused working sessions should follow these same principles in order to ensure theentire process is effective and affordable.

Focused Working SessionsThe working sessions on land use, ecology and engineering are the foundation of the wholeprocess for identifying at-risk drainage catchments and prioritizing action. For each of thefocused working sessions it is important to identify the key participants, desired outcomesand technical information that could be presented at the working sessions to help achieve thedesired outcomes. Table 5-1 summarizes this information.

It is recognized that many jurisdictions may not have access to all of the technicalinformation suggested in Table 5-1. Not all of the listed technical information is necessarilyrequired to make informed decisions. The success of the process depends mainly on the localknowledge and experience of working session participants. In the absence of hard data, it isacceptable to substitute value judgements that are knowledge-based.


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Table 5-1 Structure for Focused Working Sessions

Land Use Working Session Drainage Working Session Ecology Working Session

Desired OutcomeAn overall map of the stormwater planning area (regionaldistrict or municipality) showing the areas where there isgreatest pressure for future land use change

An overall map of the stormwater planning area (regionaldistrict or municipality) showing drainage ‘hot spots’

An overall map of the stormwater planning area (regional districtor municipality) showing aquatic habitat and species distribution

Key Participants

People who have knowledge about future land use change,including:

� planning staff representing all jurisdictions within theregional district or municipality

� First Nations� representatives from the development community

People who have knowledge about drainage problems,including:

� engineering staff representing all jurisdictions within theregional district or municipality

� operations and maintenance staff from all jurisdictions� community ratepayer associations

People who have knowledge about aquatic habitat and species,including:

� parks and environment staff representing all jurisdictionswithin the regional district or municipality

� representatives from senior government agencies (WLAP,Fisheries and Oceans Canada, Environment Canada),including habitat biologists and water quality specialists

� representatives from local stream stewardship groups andFirst Nations

TechnicalInformation

Base maps or GIS layers showing key information thataffects future land use change, including:

� OCP land use designations� zoning polygons� cadastral (lot) boundaries� growth management strategies� existing land cover characteristics, particularly

impervious areas (air photos can provide thisinformation)

� current development proposals� limits of utility servicing or ‘septic suitable’ soilsThis information should be combined with maps showingwatershed and sub-catchment boundaries. It would also beuseful to assemble air photos showing existing and historicland use patterns in order to provide a perspective on pastdevelopment patterns.

Base maps or GIS layers showing key factors that influencedrainage problems, including:

� layout of existing drainage system (storm sewers andcreeks)

� location of stream crossings, culverts and storm seweroutfalls

� location of known flooding incidents or other drainage-related problems

� floodplain mappingThis information should be combined with maps showingwatershed and sub-catchment boundaries. It would also beuseful to provide air photos that show existing land uses.

Base maps or GIS layers showing key information that affectsaquatic habitat and species, including:

� vegetation mapping, particularly for riparian areas� watercourse classification and data, including fish presence� relevant water quality data� sensitive ecosystem polygons� soils mapping� floodplain mappingThis information should be combined with maps showingwatershed and sub-catchment boundaries.For certain regions, considerable biophysical mapping hasalready been done by senior government agencies.


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5.3 Case Study: Stormwater Priorities in the RegionalDistrict of Nanaimo

The Regional District of Nanaimo (RDN) is typical of many rural/suburban regional districtsin British Columbia. The majority of the regional district is in forestry uses, with growingpockets of agriculture and urban land uses at lower elevations.

Stormwater management activities to date have been concentrated in the membermunicipalities of Nanaimo, Parksville and Qualicum Beach. These activities have beenprimarily drainage-focused, and the RDN has not played a significant role in their delivery.Furthermore, there has been little planning for stormwater management in the electoral areas,other than that associated with road drainage.

Since there are development areas in the regional electoral areas that include urban densitiesof residential, commercial and industrial land uses, there are already stormwater impacts thatlikely require attention within the RDN. Stormwater issues will be exacerbated by projectedurban growth increases in parts of the electoral areas.

Watersheds in the RDNThere are an estimated 50 watersheds within the developed areas of the RDN.

If a stormwater program were to commit to developing Integrated Stormwater ManagementPlans (ISMPs) for each of these watersheds, the program costs would be high, and politicalacceptance in this largely rural area would be problematic. Further, the benefits of such acomprehensive program would be limited for the RDN, because many of these watershedsare not at risk of urban stormwater impacts. In addition, the RDN does not have jurisdictionover forestry or agriculture land uses.

Clearly, rural regional districts like the RDN need to set priorities for stormwater planningthat focus their efforts. The At-Risk Methodology was applied in the RDN as a means ofdetermining these priorities.

Workshop Structure and MethodologyIn general, the RDN followed the workshop structure and methodology outlined in thischapter, with one exception. Whereas the Land Use Workshop was held as a separate event,the Drainage and Aquatic Habitat Workshops were combined into a single event, for sake oftime and cost efficiency and to allow for effective communication among the variousdisciplines involved in the process.

Land Use WorkshopInvited guests to the Land Use Workshop, in addition to members of a steering committee,included:

� Planners from the RDN

� Planners, Engineers and Approving Officers from member municipalities

� Approving Officers from the Ministry of Transportation and Highways

� Representatives of the Real Estate Board and local development associations

� Representatives of local agriculture associations

The agenda for the workshop included a review of stormwater management concepts, and thegeneral context and objectives of the stormwater planning process.

General mapping provided at the workshop included watershed boundaries overlaying recentairphoto information, as well as cadastral and land use designations.

Identification of Land Use ChangeWithin this general context, participants were asked by a facilitator to identify areas in theRDN where rapid land use change was expected over the next 10 years. Specifically,participants identified areas where:

� urban development is anticipated

� zoning for 1 hectare (2.5 acre) parcels or smaller is in place but not yet built out

� utility servicing for such zoning is in place or imminent


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� such land use change overlays a large portion of a drainage basin (two-thirds ormore)

� time permitting, the group was also asked to identify areas of substantialexpected re-development, as well as areas where lower density developmentsmight be expected to have stormwater impacts

To record the information put forward by the group, the facilitators applied ‘post-it’ notes tothe maps with notations. The group identified approximately twenty-one areas of rapid landuse change in a half-day workshop.

Of these twenty-one areas, ten were eliminated from further consideration by the RDN sincethey were located entirely within the boundaries of member municipalities. The remainingeleven areas were summarized and forwarded to the Drainage and Aquatic HabitatWorkshop.

There was considerable information exchange among the group, with many participantslearning of pending land use changes for the first time.

Drainage and Aquatic Habitat WorkshopIn the interest of time, the Drainage and Aquatic Habitat Workshops were combined into asingle event.

In addition to the steering committee, invited guests for the Drainage Workshop componentincluded:

� Engineers from the RDN

� Engineers from member municipalities

� Approving Officers and Operations Managers from the Ministry ofTransportation and Highways

� Engineers from the Ministry of Water, Land and Air Protection

� Representatives of local agriculture associations

� Representatives of local consulting engineering firms

Invited guests for the Aquatic Habitat Workshop component included:

� Habitat Biologists and Water Quality Biologists from WLAP� Habitat Biologists and Researchers from Fisheries and Oceans Canada� Biologists from Environment Canada and the Canadian Wildlife Service� Environmental Planners from member municipalities� First Nations� Representatives of local environmental consulting firms� Representatives of local stewardship organizations, including land trusts, field

naturalists and streamkeepers

The agenda for the Drainage and Aquatic Habitat Workshop included a review of stormwatermanagement concepts for new participants, the general context and objectives of thestormwater planning process in the RDN, and the results of the Land Use Workshop.

Mapping was presented that showed the eleven candidate study areas that resulted from theLand Use Workshop in more detail. The mapping illustrated the extent of proposed land usechange overlaid on watershed drainage boundaries and airphotos. In particular, mapping wasused to identify land use changes that would cover a large proportion of a small drainagebasin. Percentages of this expected cover were estimated. Maps also showed availableinformation on drainage sub-catchment boundaries and watercourses.

Identification of Areas at RiskWithin this general context, participants were asked by a facilitator to review and commenton drainage or habitat risks related to the eleven candidate areas. Specifically, for each of thecandidate areas, participants identified:

� areas of high risk for drainage-related problems like flooding or instream erosionand sedimentation

� risks to existing or potential fisheries and aquatic resources

After the identification of risks, participants were asked, as individuals, to rank the candidateareas by priority for integrated stormwater management (from 1 as highest to 11 as lowest).Tabulation of the results has provided the RDN with a sense of priority areas on which tofocus. The next step for the RDN will be to develop an ISMP on some of these prioritycatchments. For a detailed discussion on developing an ISMP, refer to Chapter 10.


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Reporting Results and Follow-Up QuestionnaireA third workshop was held to report the results of the process back to the participants.

This important step allowed for a presentation of the results in context along with the draftRDN five-year Stormwater Action Plan. The workshop allowed for discussion among theparticipants about the process and the results, and was especially important for discussion ofminority opinions.

The RDN also distributed a follow-up questionnaire to confirm acceptance of the process andthe results.

Strengths and Limitations of the At-Risk MethodologyThe At-Risk Methodology was useful and successful for the RDN. The great majority ofparticipants felt that it was appropriate and effective for making decisions about priorities.Strengths of the process include:

� low cost

� relative speed of decision making

� effectiveness of the process for selecting priorities and moving towards actionwithout undue delay

Limitations of the process are:

� accuracy of the process relies on the level of knowledge of individualsparticipating

� subjective nature of the process can leave it open to challenge by competinginterests

Building Support Through the Interdisciplinary Roundtable ProcessA key byproduct of the At-Risk Methodology is the transfer of information among theparticipants.

It is a rare occasion that brings together into one room the key planning, engineering andenvironmental professionals and non-government organizations from across a region.

The RDN Interdisciplinary Roundtable provided a key opportunity for presentation of currentstormwater management concepts to this interdisciplinary group. See Section 5.3 of thischapter for related information. The participants were able to understand and discuss howintegrated stormwater management would involve co-operative effort.

Communication with the Interdisciplinary Roundtable should not end with the conclusion ofthe At-Risk Methodology. The communication and access to expertise that was establishedwill be very important throughout the stormwater management process, including at both theneighbourhood and site planning scales when more detailed decisions become necessary.

A Look AheadAs the RDN moves toward approval and implementation of its Stormwater Action Plan, theunderstanding created among professionals in the region through the At-Risk Methodologyprocess will provide an important foundation for future success.


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5.4 The Role of MappingMapping the right information can provide a valuable tool to support decision making.However, mapping itself does not make the decisions; people make decisions. This is adistinction that often seems to be overlooked.

Keeping it SimpleInformation presented must be directly relevant to the desired outcome of the workingsession. Maps should help participants achieve the desired outcome rather than divertattention away from it. This is particularly important for the Interdisciplinary Roundtable,where different types of information are integrated.

The maps of land use change, aquatic resources and drainage ‘hot spots’ produced as a resultof the focused working sessions should only present the information needed to identify at-riskdrainage basins. Ideally, there should only be three maps presented at the InterdisciplinaryRoundtable, each one a distillation of the more detailed mapping presented at each of thethree focused working sessions.

Graphic Overlay versus Geographic Information System (GIS)The focused working sessions and the Interdisciplinary Roundtable rely on the overlay ofmaps with key information. This can be accomplished using:

� graphic overlay maps, or� GIS ArcView layers

Both options will achieve the same basic objective, which is to illustrate the relationshipbetween different types of information. While the data linkage and query options availablewith GIS provide greater opportunity for analysis, they also require greater time investment.

Use of Graphic Overlays Relevant relationships may be obvious from a review of map overlays, and this may providea more affordable analysis that is of equal effectiveness to the GIS data query. This isparticularly true for the Interdisciplinary Roundtable, where the emphasis should be onsimple maps that present only the relevant information. It will likely be obvious where areaswith high pressure for land use change overlap areas with high habitat value or drainage ‘hotspots’.

For smaller regional governments in particular, there is a likelihood that lack of GISresources and training will lead to stormwater inertia if too much reliance is placed ontechnical sophistication in GIS.

Application of GISFor jurisdictions that do have access to GIS, it provides a good tool for keeping accuraterecords of effective impervious area (EIA), which is a key determinant of watershed health.Using GIS, the EIA of each new development or retrofit area could be recorded at thesubdivision or building permit stage. In this way an accurate record of EIA can beestablished over time. Airphoto or map interpretation methods cannot record EIA becausethey cannot differentiate impervious area that is hydraulically disconnected.


Setting Performance Targets and Design Guidelines

Chapter Six

6.1 The Role of Performance Targets� Constant Improvement through Adaptive Management

6.2 Defining the Target Condition� Defining a Runoff Volume Target� Defining a Runoff Rate Target� Additional Performance Indicators� Achieving the Target Condition at the Site Level� Other Objectives for Managing Stream Health� A Widely Applicable Target Condition

6.3 Moving from Science to Site Design� The Need for Flexibility in Setting Performance Targets

6.4 Managing the Complete Rainfall Spectrum� Understanding the Rainfall Spectrum� The Importance of Rainfall Tiers� Components of an Integrated Strategy for Managing the Complete Spectrum of Rainfall� The Role of Continuous Simulation Modeling� Understanding Why Rainfall Capture is the Key

6.5 Methodology for Setting Performance Targets and Site Design Guidelines� Step #1: Assemble a Rainfall Database� Step #2: Define Rainfall Distribution� Step #3: Define Performance Targets for Managing the Complete Spectrum of Rainfall Events� Step #4: Translate Performance Targets into Design Guidelines that can be Applied at the Site Level� Step #5: Evaluate Source Control Options Through Continuous Water Balance Modeling� Step #6: Optimize Stormwater System Design Through Adaptive Management


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6.1 The Role of Performance Targets

Performance targets provide the foundation for implementing common sense solutions thateliminate the source of stormwater related problems. This chapter presents a cost-effectiveframework for local governments to:

� establish performance targets that reflect science-based understanding to guide earlyaction in at-risk catchments (see Chapter 5)

� translate these performance targets into design criteria and guidelines that can beapplied at the site level to design stormwater systems that mitigate the impacts ofland development

Performance targets provide a starting point to guide the actions of local government in theright direction. Site design criteria provide local government staff and developers withpractical guidance for moving from planning to action.

For a performance target to be implemented and effective, it must be quantifiable. It mustalso have a feedback loop so that adjustments and course corrections can be made over time.To be understood and accepted, a performance target needs to synthesize complexity into asingle number that is simple to understand and achieve, yet is comprehensive in its scope. Arunoff volume-based performance target fulfils these criteria. This chapter presents amethodology for setting volume-based performance targets.

Volume-based thinking is an integral element of a paradigm-shift that views watersheds as afully integrated system where creek headwaters originate at rooftops and roads. Lookingahead to the GVRD case study results presented in Chapter 7, the implications are far-reaching because a volume-based approach to stormwater management touches on virtuallyevery aspect of land use planning and site design. Volume-based thinking leads directly intolandscape architecture, green roofs, urban reforestation, interflow and groundwater recharge,and water re-use.


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Constant Improvement through Adaptive ManagementPerformance targets and design criteria provide a basis for:

� integrating appropriate stormwater management policies with land use andcommunity planning (see Chapter 4)

� selecting appropriate site design practices to reduce runoff and improve water qualityat the source (see Chapter 7)

The policies and site design practices implemented in at-risk catchments becomedemonstration projects. Monitoring the performance of these demonstration projectsprovides the foundation for adaptive management, as illustrated in Figure 6-1.

The goal of adaptive management is to learn from experience and constantly improve landdevelopment and stormwater management practices over time. This requires ongoingmonitoring of demonstration projects to assess progress towards performance targets and theshared watershed vision. The details of adaptive management are discussed further inSection 6.5.

Figure 6-1


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6.2 Defining a Target ConditionA biophysically-based target condition can be established based on an understanding of thecharacteristics of a healthy watershed.

In order to be achievable, a biophysically-based target condition must be translated intoperformance targets that can be applied to stormwater management practice.

Since changes in Water Balance and hydrology are the primary source of stormwater relatedimpacts on watershed health (see Chapter 2), it is especially important to establishperformance targets for managing:

� Runoff Volume, and

� Runoff Rate

Defining a Runoff Volume TargetRecent research from Washington State shows that stormwater related impacts on streamhealth start to occur once the impervious percentage of a watershed exceeds about 10% (seeChapter 2). Therefore, to ensure the health of aquatic systems, developments should beplanned and built to function like watersheds with less than 10% total impervious area.

Stormwater-related impacts are a direct result of runoff from impervious surfaces that aredirectly connected to a storm drainage system or to downstream watercourses (often definedas effective impervious area (EIA)).

The Washington State research is based on data from watersheds with traditional ditch andpipe systems designed to remove runoff from impervious surfaces as quickly as possible, anddeliver it to receiving waters.

When the impervious area of watersheds with traditional ditch and pipe systems reaches the10% threshold, about 10% of the total rainfall volume becomes runoff that enters receivingwaters; this runoff volume is the root cause of aquatic habitat degradation. Note that there isvirtually no surface runoff from the naturally vegetated portion of a watershed, but nearly allrain that falls on directly connected impervious surfaces becomes runoff.

An appropriate performance target for managing runoff volume is to limit total runoff volumeto 10% (or less) of total rainfall volume. This means that 90% of rainfall volume must bereturned to natural hydrologic pathways, through infiltration, evapotranspiration or re-use onthe development site. Managing 90% of the rainfall volume throughout a watershed shouldachieve the biophysical target condition for the watershed. Managing 90% of rainfall volumetherefore becomes the volume-based performance target.

Defining a Runoff Rate TargetAs discussed in Chapter 2, the Mean Annual Flood (MAF) is defined as the channel-formingevent; as the MAF increases with development, stream channels erode to expand their cross-section, thereby degrading aquatic habitat. Therefore, an appropriate runoff rate target is toensure that streamflow rates that correspond to the natural MAF occur no more than once peryear, on average.

In order to achieve this target, stormwater systems should be designed to limit the frequencythat the natural MAF is exceeded.

The MAF correlates roughly with the runoff from a Mean Annual Rainfall (MAR), which isdefined as the rainfall event that occurs once per year, on average. The significance of theMAR is discussed further in Section 6.4.

Natural streamflow patterns can be approximated for the majority of rainfall conditions (allrainfall in an average year) by providing enough storage capacity to capture the runoff from aMAR, and releasing the stored runoff at a rate that mimics the rate of interflow in a naturallyvegetated watershed.


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Additional Performance IndicatorsAs discussed in Chapter 2, there are additional science-based indicators that could be used asperformance targets for protecting watershed health, including:

� Maintain stream baseflow at a minimum of 10% of the Mean Annual Discharge(MAD).

� Maintain natural total suspended solids (TSS) loading rates.� Maintain key indicators of aquatic ecosystem health (e.g. maintain Benthic Index of

Biological Integrity (B-IBI) score above 30).� Preserve a 30-metre wide intact riparian corridor along all streamside areas.� Retain 65% forest cover across the watershed.

These indicators of watershed health can play an important role in comprehensiveperformance monitoring and adaptive management programs (as discussed in Section 6.5).

These indicators may also be used to help define a biophysically-based target condition for ahealthy watershed. The GVRD’s Integrated Stormwater Management Planning Terms ofReference Template (2002) provides an example of how some these indicators have beenapplied to define a target condition.

This Guidebook presents a methodology for setting performance to achieve the runoffvolume target (i.e. limiting runoff volume to 10% of total rainfall) and runoff rate target (i.e.maintaining natural MAF). The runoff volume and rate targets have been selected as theprimary basis for defining a biophysically-based target condition to guide stormwaterplanning and design because:

� They are based on scientifically defensible research that correlates watershedimperviousness and changes in hydrology with stream health.

� They provides an easily understood starting point for the design of stormwatersystems at the site level (as described in this chapter). These targets can be directlymanaged at the site level.

� Achieving the 10% volume target should also achieve management objectives forstream baseflows, water quality and aquatic ecosystem health. This is a reasonableassumption because:

� Infiltrating rainfall at the source is the most effective way to maintain streambaseflows.

� Infiltration and other stormwater source control strategies provide effectivetreatment for the first flush of pollutants that wash off from developed areas.

� Restoring the natural Water Balance eliminates the source of stream degradationand improves aquatic ecosystem health.

Monitoring the performance of demonstration projects will provide the opportunity to testhow well alternative performance targets relating to baseflows, water quality and aquaticecosystem health can be managed by achieving the runoff volume and rate targets (seeSection 6.5).


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Achieving the Target Condition at the Site LevelDegradation of watershed health is the result of the cumulative impact of individual landdevelopment projects on runoff volume and rate (i.e. incremental changes in Water Balanceand hydrology). Each development project contributes to increased runoff volume and rate indownstream watercourses.

In order to achieve the target condition for a healthy watershed as a whole, cumulativeimpacts must be managed at the site level. This means that stormwater systems at the sitelevel must be designed to achieve to achieve the runoff volume and rate targets.

The Role of Source ControlTo achieve runoff volume and rate targets, development sites and their stormwater systemsmust be designed to replicate the functions of a naturally vegetated watershed (the mosteffective stormwater system). This requires stormwater source control strategies that capturerainfall at the source (on building lots or within road right-of-ways) and return it to naturalhydrologic pathways - infiltration and evapotranspiration - or re-use it at the source. Thiscreates hydraulic disconnects between impervious surfaces and watercourses (or stormdrains), thus reducing the volume and rate of surface runoff.

Looking ahead, Chapter 7 presents a variety of source control solutions for maintaining orrestoring natural runoff volume and rates, including:

� Preserving natural vegetation cover, natural stormwater management features (e.g.wetlands), and limiting the extent of impervious areas through low impactdevelopment practices

� Preserving or restoring natural infiltration capacity by infiltrating runoff fromimpervious surfaces and applying absorbent landscaping

� Preserving or restoring natural evapotranspiration capacity to the extent possiblethrough conservation, landscaping and the application of green roofs

� Re-using rainwater for irrigation and for indoor uses

Chapter 7 provides guidance for selecting appropriate source control strategies for differentland use types, soil conditions and rainfall characteristics.

Other Objectives for Managing Stream HealthTo maintain or restore stream health, this Guidebook recommends focusing limited resourceson managing runoff volume and rate. Scientific research on the subject recommends a broadrange of strategies including:

� Preserve or restore natural vegetation along riparian corridors.

� Preserve or restore natural features, such as wetlands, that play a key role inmaintaining the hydrologic and water quality characteristics of healthy streams.

� Preserve or restore instream features that are key to the health of aquatic ecosystems,such as channel complexity and adequate spawning gravel.

� Control sources of water pollution (point and non-point sources).

Integrated Stormwater Management Plans (ISMPs) should address these objectives, inaddition to the runoff volume and rate targets.

Desired Outcomes for ISMPsIntegrated stormwater management plans (ISMPs) for individual watersheds should therefore:

� establish objectives for maintaining and/or restoring stream health

� develop comprehensive strategies to achieve these objectives, which not only dealwith runoff volume and rate, but also address issues relating to water quality andpreservation/restoration of key natural features (e.g. riparian forests, wetlands, in-stream features)

The elements of ISMPs are discussed further in Chapter 10.


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A Widely Applicable Target ConditionThe fact that performance targets are based on the characteristics of a healthy watershed iskey. This means that the performance targets for any given watershed apply to:

� new development or retrofit scenarios - Appropriate land development practices canprevent the degradation of a healthy watershed or restore an unhealthy watershed.The target condition remains the same.

� protection of environment or property - Maintaining or restoring the ecological healthof a watershed will also eliminate the source of flooding risk to property and publicsafety. Protecting aquatic resources and protecting property are complementaryobjectives. Even if property impacts are the driver for action, biophysically-basedperformance targets are still appropriate.

The Range of Case Study ExperienceThe methodology presented in this chapter for setting performance targets and design criteriaevolved through recent integrated stormwater management experiences in British Columbia.Preliminary performance targets and site design criteria were developed using thismethodology in three different catchments, all with different initial conditions, developmenttypes and drivers for action. The three case studies included the following developmentscenarios:

� Urban - High-density urban development at the top of a mountain, where protectionof downstream aquatic habitat was the primary driver for action.

� Suburban - Fully developed suburban watershed, where the need for immediateflood relief was the driver for action.

� Suburban/Rural - A municipality comprising rural and suburban land uses, wherefuture development areas (currently forested) drains to agricultural lowlands.Aquatic habitat protection was also a driver.

The methodology has been tested and accepted by the local governments in all three cases.The suburban/rural example (City of Chilliwack) is used as a case study for the remainder ofthis chapter to illustrate the methodology.


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6.3 Moving from Science to Site DesignAs shown below, the biophysically-based target condition provides a basis for acomprehensive stormwater management strategy (see Figure 6-3). Performance targets andsite design criteria are needed to translate this strategy into action at the site level.

Biophysically-Based Target ConditionThe target condition is based on the characteristics of a healthy watershed, and incorporates targetsfor maintaining the natural Water Balance (restore 90% of rainfall volume to natural hydrologicpathways) and hydrology (maintain natural MAF). Other characteristics of a healthy watershed (e.g.water quality, baseflow, riparian integrity) may also help define a target condition.

Science-Based Performance Targets and Site Design Criteria

Translating the above strategy into an action plan requires performance targets and designcriteria to guide stormwater management and development practices at the site level.Performance targets and design criteria can be evaluated and optimized to reduce costsover time by monitoring the performance of demonstration projects.

Science Based Strategy for Managing the Complete Spectrum ofRainfall Events

Stormwater impacts occur when land use change alters the water balance, thus increasing thevolume and rate of surface runoff from every rainfall event. In order to maintain or movetowards the target condition, the complete spectrum of rainfall events must be managed in amanner that approximates a naturally vegetated watershed.

Leads to:

Figure 6-2

Implementingthis strategy

requires:

InfrequentLarge Storms(up to MAR)

FrequentSmall Storms

(less than half of MAR)

RareExtreme Storms

(greater than MAR)

Site-Specific Rainfall Distribution(relative to MAR, the site-specific mean annual rainfall)

Infil

trat

ion

Rainfall Capture

DeepGroundwater

Evaporation-Transpiration

Infiltrate or Reuse Small Storms at the Source to Reduce

Total Runoff Volume

Reuse

Runoff

Provide DetentionStorage to

Control the Rate of Runoff from Large Storms

StorageRelease

Rate TargetThe natural

Mean Annual Floodis maintained

Controlled Flow

Ensure that the Stormwater Systemcan Safely Convey

Extreme Storms


Volume Target90% of total rainfall volume is returned to

natural hydrologic pathways

Runoff Control


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The Need for Flexibility in Setting Performance TargetsEstablishing performance targets provides a quantifiable way of measuring success inprotecting or restoring a watershed, and for identifying what needs to be done to achieve acertain level of protection for a given watershed.

The runoff volume and rate targets presented in presented in Section 6.2 provide a referencepoint that is based on the Water Balance and hydrology of a healthy watershed. To determinewhether these targets are realistic or achievable for a given watershed, an ISMP must answerthe following questions:

� What is the existing level of annual runoff volume? What percentage of total annualrainfall volume does it represent? What is the existing Mean Annual Flood (MAF)?

� What are acceptable levels of runoff volume and rate in terms of flood risk andenvironmental risk? What are the consequences of increased or decreased flowsrelated to land development? Are these consequences acceptable?

� What actions are needed to avoid flooding or environmental consequences?

� How can necessary actions be staged over time?

� Are the targets to maintain 10% runoff volume and maintain the natural MAFnecessary or achievable over time? If not, what levels are?

Performance targets that are based on the characteristics of a healthy watershed, includingtargets for runoff volume, runoff rate, and any other indicators that may be used to define atarget condition, should be used as a starting point. Performance targets should becustomized for individual watersheds and catchments, based on what is effective andaffordable in the context of watershed-specific conditions.

For example, the 10% runoff volume target may not be appropriate for a watershed withlimited fisheries value. In this case it may be more appropriate to establish targets forreducing the volume and rate of runoff based on judgements regarding acceptable levels offlooding.

Continuous Water Balance modeling can be applied to determine what is effective andaffordable. Further discussion of Water Balance modeling is found in Chapter 7.


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6.4 Managing the Complete Rainfall SpectrumA guiding principle of integrated stormwater management is to design for the completespectrum of rainfall events (as shown in Figure 6-2). Designing for the complete spectrum ofrainfall events provides the foundation for protecting both property and stream health.

Understanding the Rainfall SpectrumA key parameter for describing the rainfall spectrum is the size of the Mean Annual Rainfall(MAR), the rainfall event that occurs once per year, on average. The distribution of rainfallevents relative to the MAR is fairly constant throughout British Columbia.

The following rainfall tiers are the building blocks of an integrated strategy for managing thecomplete spectrum of rainfall events:

� Tier A Events* – The small rainfall events that are less than half the size ofa MAR. About 90% of all rainfall events are Tier A events.

� Tier B Events* – The large rainfall events that are greater than half the sizeof a MAR, but smaller than a MAR. About 10% of all rainfall events are Tier Bevents.

� Tier C Events* – The extreme rainfall events exceeding a MAR. Anextreme event may or may not occur in any given year.

* For the purpose of setting performance targets, a rainfall event is defined as total daily rainfall(i.e. mm of rainfall accumulated over 24 hours). This assumption results in conservative sitedesign criteria, which can be optimized over time through continuous simulation modeling, and bymonitoring the performance of demonstration projects (as discussed in Section 6.5).

These three rainfall tiers correspond to three components of an integrated strategy formanaging the complete spectrum of rainfall events (see Figure 6-2); rainfall capture (sourcecontrol), runoff control (detention), and flood risk management (contain and convey). Thesethree components are discussed further in this section.

The Importance of Rainfall TiersDefining tiers is the key to the rainfall analysis. It enables a systematic approach to dataprocessing and identification of rainfall patterns, distributions and frequencies. Establishingthe MAR as a reference point provides a convenient way to divide the rainfall database intothree groupings.

Table 6-1 below shows how the rainfall tiers vary across the regions of BC where the mostdevelopment is occurring. In the Georgia Basin the MAR ranges from about 40 mm on theEast Coast of Vancouver Island, to about 60 mm in the Fraser Valley (also representative ofmuch of the Lower Mainland), to about 80 mm on the North Shore of Vancouver. For theOkanagan Region, the MAR is closer to 20 mm.

Table 6-1 – Rainfall Spectrum for Various Locations in BC

Location Tier A Events(less than 50% of

MAR)

Tier B Events(between 50% ofMAR and MAR)

Tier C Events(Greater than MAR)

Vancouver(North Shore)

< 40 mm 40 to 80 mm > 80 mm

Chilliwack < 30 mm 30 to 60 mm > 60 mm

Nanaimo < 20 mm 20 to 40 mm > 40 mm

Kelowna < 10 mm 10 to 20 mm > 20 mm

* approximate values based on statistical analyses using of 30+ years of rainfall data

One of these examples (Chilliwack) is used throughout this chapter to illustrate how to:� use rainfall data to define MAR and the rainfall tiers� apply the rainfall tiers to establish performance targets and site design guidelines


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Managing Rainfall Volume at the SourceTier A events make up the bulk of total annual rainfall events and rainfall volume (seeFigures 6-3 and 6-4). Capturing these small events at the source is the key to reducing runoffvolume and managing the Water Balance (i.e. rainfall capture).

Figures 6-3 and 6-4 illustrate both coastal and interior conditions. Regardless of location, themajority of rainfall events are small (less than 50% of MAR). This is a key observation withrespect to the feasibility of approximating the natural Water Balance through infiltrationand/or rainfall re-use.

Consistency with Current Stormwater PracticeReferencing the rainfall tiers to the Mean Annual Rainfall (MAR) provides consistency withcriteria that became accepted practice in the 1990s.

In British Columbia, the Land Development Guidelines for the Protection of Aquatic Habitat(1992) focus on managing runoff from storms with a 2-year return period, which isapproximately equal to the MAR.

Also, 50% of the MAR corresponds to what is called a ‘6-month storm’ in Washington State.The concept of the ‘6-month storm’ was introduced in Washington to provide context formanaging the six to ten runoff events per year that have the most potential to causewatercourse erosion (i.e. Tier B events). At the time, this approach represented a majordeparture from traditional drainage practice.

Prior to the late 1990s, the focus of drainage planning was on the extreme events that rarelyoccurred (Tier C events).

The tiered approach marks a further shift in drainage practice, from managing 25% of therainfall volume (Tier B and C) to managing 100% of the rainfall (i.e. the completespectrum).

74% 71%

21% 23%

4 % 6%

0

2 0

4 0

6 0

8 0

1 0 0

Pe

rce

nt

of

To

tal

An

nR

ain

fall

L e s s th a n 5 0 % o fM A R

5 0 % o f M A R to M A R G re a te r th a n M A R

R a in fa ll E v e n t S iz e (m m )

T y p ic a l V o lu m e D is tr ib u tio n o f A n n u a l R a in fa ll

S o u th C o a s t (B u rn a b y M o u n ta in ) O k a n a g a n (K e lo w n a A irp o rt)

N ote : B urnab y M oun ta in M A R * = 70 m m K e low na M A R * = 20 m m (*2 4 -h o u r ra in fa ll )

Figure 6-4

160

97

8 5 1 1

0

50

100

150

200

No. R

ainf

all E

vent

s pe

r Yea

r

Less than 50% of MAR 50% of MAR to MAR Greater than MAR

Rainfall Event Size (mm)

Typical Frequency Distribution ofAnnual Rainfall

South Coast (Burnaby Mountain) Okanagan (Kelowna Airport)

Note: Burnaby Mountain MAR* = 70 mm Kelowna MAR* = 20 mm

(*24-hour rainfall)

Defined as Tier A Events.

Defined asTier B Events Defined as

Tier C Events

Figure 6-3


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Components of an Integrated Strategy for Managing the CompleteSpectrum of Rainfall

Each of the three rainfall tiers corresponds to a component of an integrated strategy:

1. Rainfall Capture (Source Control) to Manage the Small Tier A Rainfall EventsThe key to runoff volume reduction and water quality improvement is capturing the smallstorm runoff (Tier A rainfall events) from rooftops and paved surfaces. This capturedrainfall should be infiltrated, evapotranspired, and/or re-used at the source. Rainfallcapture can be provided at the source with:

� On-lot stormwater source control facilities to capture runoff from rooftops,driveways, parking and other impervious areas for infiltration, evapo-transpirationand/or reuse.

� On-street source control facilities to capture and infiltrate runoff from pavedroadways. These facilities must also be designed to convey extreme storms, similarto conventional storm sewers.

Chapter 7 describes specific source control options available for development parcels androads, including specific examples.

2. Runoff Control (Detention) to Manage the Large Tier B Rainfall EventsThe runoff resulting from the large Tier B events causes the most significant peak flowsin downstream watercourses. Therefore, the key to runoff rate control is storing therunoff from impervious surfaces resulting from the large Tier B rainfall events andreleasing it at a controlled rate. This controlled release will eliminate the ‘spikes’ thatcharacterize the rapid response of runoff from impervious surfaces. Storage capacity forlarge Tier B storms can be provided:

� By increasing the storage capacity of on-parcel and on-street source control facilities(above the capacity required to achieve rainfall capture targets).

� In community detention facilities that serve sub-catchments of a watershed (canprovide runoff control but not rainfall capture).

3. Flood Risk Management (Contain and Convey) for the Extreme Tier C RainfallEvents

Development sites must have adequate escape routes for runoff from extreme storms(combination of overland flow and flow collection and conveyance systems). Streamchannels and stream crossing (e.g. culverts and bridges) must have sufficient capacity tocontain and convey flood flows resulting from very large storms (e.g. the 100-yearstorm), without resulting in threats to public safety or property damage. A framework forflood risk management is presented in Section 6.5.

The Role of Continuous Simulation ModelingPerformance targets (i.e. a starting point) can be established based on simple rainfall analysis(see Section 6.5). The level of effort required to apply continuous simulation modeling is notappropriate for setting performance targets, but is appropriate for optimizing design solutionsto achieve the performance targets.

As explained in Chapter 7, continuous simulation modeling is also appropriate for evaluatingstormwater source control options and optimizing the design of stormwater systemcomponents.


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Understanding Why Rainfall Capture is the KeyRunoff control without rainfall capture is the conventional detention-based approach tostormwater management. It is only a partial solution. It is now recognized that this approachdoes not protect downstream fish habitat because it does not maintain natural levels oferosion or support baseflows in watercourses.

The water released from conventional detention storage typically goes directly to downstreamwatercourses. This slows down the water and reduces peak runoff rates, but does not reducethe total runoff volume. Therefore, the total runoff volume is spread out over a longer periodof time, which can result in erosive streamflows for longer periods of time.

Rainfall capture requires storage at the source, where runoff from impervious surfaces can beinfiltrated into the ground, evapotranspired, or re-used rather than released directly to surfacedrainage systems. Infiltration not only reduces runoff volume, but also supports streambaseflow by partially restoring the natural Water Balance.

Detention facilities that serve sub-catchments of a watershed do not provide the opportunityfor infiltration, evapotranspiration or re-use at the source. However, there may beopportunities to implement community source control facilities through neighbourhoodplanning (e.g. infiltration facilities that serve multiple dwelling units).

The objective of emphasizing rainfall capture is to place the stormwater management focusclearly on volume. Traditional drainage practice concentrated on peak flow rates andoverlooked the importance of volume management.

The Importance of Rainfall Capture for Water QualityRainfall capture is important for improving water quality as well as for reducing runoffvolume. The objective of rainfall capture is to infiltrate small storms and the first portion oflarge storms at the source. This means that the ‘first flush’ of pollutants that get washed offimpervious surfaces at the beginning of rainfall events will be filtered and receive sometreatment as they infiltrate into the ground.

Rainfall that is captured at the source for re-use may require a certain amount of treatment,depending on its intended use. Indoor uses, such as toilet flush water, would likely requiresome form of treatment to satisfy regulatory requirements for public health protection.


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6.5 Methodology for Setting Performance Targets andSite Design Guidelines

Case Study Example: City of ChilliwackThe City of Chilliwack is used as a case study in this section to demonstrate how to setperformance targets and translate these targets into site design criteria. Chilliwack hasapplied a 6-step process for setting performance targets and developing site design criteria(see Figure 6-5). These steps are described in this section.

Chapter 4 showed how Chilliwack has integrated performance targets with stormwatermanagement policies. This is a first step towards integrating targets with the OfficialCommunity Plan.

Chapter 7 elaborates on how Chilliwack has translated performance targets into a series ofDesign Guidelines for Stormwater Systems that developers can apply at the site level.

Chilliwack started applying the Guidebook methodology in the spring of 2001. Over the yearthat followed, the Chilliwack case study provided an opportunity to test, validate and refinethe Guidebook methodology. This process was undertaken in an inter-departmental andinter-agency environment, and used actual land development projects in the City to apply themethodology. The interaction with the development community was essential to making themethodology practical.

Tier B Storms50% MAR to MAR*

= 30 to 60 mm

Tier A Storms less than 50% MAR*

= up to 30 mm

Tier C Storms> MAR*

= greater than 60 mm

Step #2 – Define Rainfall Distribution* In the Chilliwack region, the MAR for a 24-hour duration is 60 mm.

Rainfall Capture(runoff volume reduction)

Runoff Control(runoff rate control)

Capture the first 30 mm of rainfall perday at the source (i.e. lots and roads)for infiltration, evapotranspiration or

re-use

Detain the next 30 mm of rainfall perday (storms up to 60 mm) and releaseto storm sewers or streams at a rate

that mimics natural interflow*


Ensure that the stormwatersystem can safely convey

storms greater than 60 mm(up to 100-year flood)

Step #3 – Define Performance Targets for Managing the Complete Spectrum of Rainfall

Step #4 – Translate Performance Targets into Design Guidelinesthat can be Applied at the Site Level

Step #6 – Optimize Stormwater System Design Through Adaptive Management

* Rate of release should replicate the interflow (or baseflow) from a natural forested area equal to thearea served by the runoff control facility. For the Chilliwack region this rate is about 1 Lps per hectare.

Step #5 – Evaluate Source Control Options ThroughContinuous Water Balance Modeling

Step #1 - Assemble a Rainfall Database

Figure 6-5


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Step #1 - Assemble a Rainfall DatabaseRainfall data is readily available in most jurisdictions. Environment Canada operates anextensive network of rainfall gauging stations across the province. Many regional districtsand municipalities are beginning to operate their own stations, and in some cases localgovernment-operated networks are in place.

Rainfall data should be obtained from a gauging stations as close as possible to the watershedwhere performance targets are being set.

Obtaining rainfall data from several stations in a region can provide a good idea of rainfallvariability and enable the establishment of regional performance targets (as shown in theChilliwack example).

For establishing performance targets, a rainfall data set should have a period of record that islong enough to enable statistical analysis (longer is better). The rainfall data must be put intoa spreadsheet format to enable the necessary analysis (described on the following page).

A key principle is to assemble the best rainfall data available (i.e. longest period of record,closest to watersheds of interest) and to use this data to establish performance targets.

Even in the absence of rainfall data, the example rainfall tiers shown in Table 6-1 (from therelevant region) can be used to develop performance targets that provide a reasonable startingpoint for action. The values in Table 6-1 can also provide a check on analyses performedusing data from rain gauges with short periods of record.

Daily versus Hourly Rainfall DataDaily rainfall data is adequate for the basic analysis needed to set preliminary performancetargets and site design criteria. However, hourly rainfall data provides a better description oflocal rainfall characteristics. Certain rainfall characteristics, such as rainfall intensity, can notbe established based on daily data. Hourly data also enables more detailed monitoring andmodeling (see Step #5 and #6).

Climate Change ConcernsClimate change projections show that total winter rainfall is likely to increase over time (thusincreasing total runoff volume), and that the frequency of short intense storms, orcloudbursts, is also likely to increase. Chapter 7 shows how the implementation ofstormwater source control strategies can mitigate the impacts of climate change.

Performance targets provide a starting point for evaluating source control options. It does notmatter that these targets are based on historic rainfall data.

Case Study Example: Assembling Rainfall Data

Long-term rainfall data is available from three Environment Canada rainfall gauging stationsin the greater Chilliwack area:

� Agassiz (on the north side of the Fraser River) – 109 years of record

� Sardis (near Vedder crossing) – 46 years of record

� Chilliwack (between Chilliwack City Center and Highway 1) – 90 years ofrecord

Rainfall data from these three stations were used to establish general performance targets forthe Chilliwack region. These targets can be customized for individual sub-catchments withinthe region by monitoring the performance of demonstration projects (see Step #6).

Since April 1999, the City has been operating two continuous rain gauges on a hillside areaabove the agricultural lowlands that is designated for future land development. These gaugesare important for monitoring the change in rainfall-runoff response as land developmentprogresses on the hillsides, and thus evaluating how well particular site design practices aremitigating the impacts of land development.


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Step #2 – Define Rainfall DistributionThe rainfall event categories (Tier A, Tier B, and Tier C) form the basis for settingperformance targets and developing site design criteria to manage the complete spectrum ofrainfall events. In order to define the thresholds for these categories, the Mean AnnualRainfall (MAR) must be determined.

Methodology for Defining Mean Annual Rainfall (MAR)The MAR for any watershed can be defined through the following process:

1. Calculate the peak daily rainfall (24-hr rainfall depth) for each year of record fromthe rainfall gauge. This can be done with a simple spreadsheet function.

2. Rank the rainfall maxima from highest to lowest and calculate a return period (T) foreach using a standard plotting position formula (e.g. Weibull formula, T = [total # ofrainfall maxima + 1]/rank).

3. Create a logarithmic plot of rainfall maxima vs. return period.

4. From this plot determine the rainfall maxima with a 2-year return period (R2). This isapproximately equal to the MAR (the statistical definition of MAR is the rainfall witha 2.33 year return period).

Since the preceding methodology is a statistical analysis, a long period of record (30 years ormore) will ensure confidence in the results.

Defining Rainfall TiersOnce the site-specific MAR is determined, rainfall event categories can be defined:

� Tier A = less than 50% of MAR� Tier B = 50% MAR to MAR� Tier C = greater than MAR

Illustrating the Rainfall DistributionThe site-specific rainfall frequency distribution (see Figure 6-3) can be determined byapplying a spreadsheet query to the rainfall database (count the total # of Tier A, Tier B, andTier C events). This will validate that the majority of rainfall events are small.

The site-specific rainfall volume distribution (see Figure 6-4) can also be determined usingspreadsheet functions (add up the total depth of Tier A, Tier B, and Tier C events). This willvalidate that the small Tier A events account for the majority of total annual rainfall volume.


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Case Study Example: Defining Rainfall DistributionThe MAR (24-hour duration) for Chilliwack was determined using data from the three long-term rainfall gauging stations. The points plotted on Figure 6-6 represent the peak annualrainfall event (24-hr rainfall depth) for each of the 90 years of record from the Chilliwackrainfall gauge. The same analysis was performed using the Sardis rainfall gauge and theAgassiz rainfall gauge.

Based on this analysis, the MAR at each of the three stations was determined to be:

� Chilliwack = 63 mm� Agassiz = 60 mm� Sardis = 55 mm

Therefore, the regional MAR for the Chilliwack area can be defined as 60 mm (over 24 hrs).This regional approximation provides the basis for specifying the following rainfall tiers:

� Tier A = less than 50% of MAR = less than 30 mm� Tier B = 50% MAR to MAR = 30 mm to 60 mm� Tier C = greater than MAR = greater than 60 mm

Chilliwack Rainfall AnalysisReturn Period Analysis - Daily Rainfall Maxima

0102030405060708090

100110120130140150160170180190

1 10 100

Return Period (yrs)

Peak

Ann

ual D

aily

Rai

nfal

l (m

m)

MAR ~ R2

MAR = 63 mm

Figure 6-6


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Step #3 – Define Performance Targets for Managing theComplete Spectrum of Rainfall EventsThe rainfall tiers, established in Step #2, must be translated into performance targets forrainfall capture, runoff control and flood risk management.

Case Study Example: Translating Tiers into TargetsThe City of Chilliwack’s performance targets are presented below to illustrate how rainfalltiers translate into performance targets.

Rainfall Capture Performance Targets (for Tier A Events)

Capture the first 30 mm of rainfall per day (24 h) at the source (i.e. lots and roads) andrestore to natural hydrologic pathways (infiltration and evapotranspiration) and/or re-use.

This relates to the following specific rainfall capture targets:

� For impervious areas – Provide stormwater source control facilities* on developmentlots, roads or neighbourhood sites that are designed to capture 30 mm of rainfall per day,and either infiltrate, evapotranspire, or re-use the captured rainfall.

� For pervious areas – Preserve as much undisturbed natural area as possible. Forlandscaped areas, provide an absorbent surface soil layer that has the capacity to storeat least 60 mm of rainfall and infiltrate at the natural rate of local soils. This will ensurethat pervious areas produce virtually no surface runoff (much like a naturally vegetatedwatershed).

* the selection and design of source controls must be based on site-specific conditions (see Steps #4 and #5)

Runoff Control Performance Targets (for Tier B Events)

Detain the next 30 mm per day (all rainfall events up to 60 mm over 24 h) and release tostorm sewers or stream channels at a rate that approximates a natural forestedwatershed.

This relates to the following specific runoff control target:

� For impervious areas – Provide enough storage volume to detain the runoff resultingfrom rainfall events up to 60 mm per day, either in rainfall capture facilities and/orcommunity detention facilities. Release the stored rainfall at a rate that replicates theinterflow from a natural forested area* (equivalent to the area served by the runoff controlfacility).

� For pervious areas – Meeting the rainfall capture target also provides adequate runoffcontrol (i.e. enough storage for 60 mm of rainfall).* natural interflow can be defined based on streamflow monitoring in undeveloped catchments (see Step #4)

Flood Risk Management Performance Target (for Tier C Events)

Ensure the stormwater system is capable of safely conveying an extreme flood event thatresults from rainfall events greater than 60 mm (e.g. the 100-Year Flood, Q100).

The runoff from extreme storms must be conveyed, through a combination of overland flowpaths and flow collection and conveyance systems, without causing property damage, posing athreat to public safety, or causing unacceptable levels of flooding in agricultural areas.


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Validating Performance TargetsAs discussed in Section 6.2, achieving the biophysically-based target condition (a healthywatershed) means that 90% of total rainfall volume must be captured at the source to reducetotal runoff volume to 10% or less of total rainfall volume.

Figure 6-7 relates the performance targets for rainfall capture, runoff control and flood riskmanagement to rainfall volume distribution (at the Sardis gauge).

The same analysis was performed using data from the other two long-term rainfall stations(Chilliwack and Agassiz). The volume distribution for all three stations is summarizedbelow.

Rainfall Station Rainfall CaptureVolume

Runoff ControlVolume

Flood ControlVolume

Chilliwack 89% 7% 4%Agassiz 91% 6% 3%Sardis 93% 5% 2%

Capturing the first 30 mm of rainfall per day (i.e. meeting Chilliwack’s rainfall capturetarget) would result in capture of about 90% of the total volume of runoff from imperviousareas. Also, implementing absorbent landscaping practices can virtually eliminate runofffrom pervious areas (i.e. achieve close to 100% capture), as discussed in Chapter 7.

The key point is that meeting rainfall capture targets should achieve the biophysically-basedtarget condition.

0

200

400

600

800

1000

1200

Tota

l Ann

ual R

ainf

all (

mm

)

less than 30 mm 30 mm to 60 mm greater than 60 mm

Rainfall Event Size

Distribution of Annual Rainfall Volum e (Sardis)

Rainfall Capture Volume (93%) Runoff Control Volume (5%) Flood Control Volume (2%)

Figure 6-7


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Step #4 – Translate Performance Targets into DesignGuidelines that can be Applied at the Site LevelIn order to achieve performance targets for rainfall capture, runoff control and flood riskmanagement, the targets must be translated into achievable design guidelines that developersand local government staff can understand and apply at the site level.

Design Guidelines for Rainfall Capture (Managing Tier A Events)Reducing runoff volume is the key to achieving performance targets for rainfall capture. Thefollowing volume reduction strategies should be applied:

� Minimize the disturbance of natural soils and vegetation. At the land use planningand site design levels, it is important to identify and preserve the natural areas that aremost important to maintaining the natural Water Balance, such as wetlands, naturalinfiltration areas and riparian forests. Low impact site design practices that limit thecreation of impervious area, the compaction of natural soils and the clearing of naturalvegetation should also be applied.

� Apply absorbent landscaping. For landscaped areas, an absorbent surface soil layershould be provided. This absorbent soil layer should:

� be deep enough to store the mean annual rainfall (24-h duration). Since mostabsorbent soils store about 20% of their volume in soil water, five times theMAR is an appropriate soil depth (e.g. for Chilliwack this would be 60 mm x 5 =300 mm).

� meet the BC Landscape Standard for medium or better landscape, which willensure the type of hydrologic characteristics required for rainfall capture.

� Implement stormwater source control practices to capture runoff from impervioussurfaces. Source control options include:

� Infiltration Facilities – Infiltration is likely the only way achieve the targetcondition of restoring 90% of total rainfall volume to natural hydrologicpathways, and is the most appropriate source control for single family land uses,which is the dominant land use in most developed watersheds in the province.

The level of reduction in the volume and rate of runoff that is achievable usinginfiltration depends on soil conditions, and therefore, soils information is key tothe planning and design of infiltration facilities.

� Green Roofs – The volume and rate of rooftop runoff can be reduced by installingabsorbent landscaping on rooftops of buildings or parkades. Green roofs willstore and evapotranspire rainfall from small events, and will slow the rate ofrelease of medium-sized events. Green roofs are most effective for land useswith high levels of rooftop coverage, such as multiple family and commercialland uses (especially with underground or structured parkades).

� Rainwater Re-use – Capturing and re-using rooftop runoff for greywater uses (e.g.toilets, laundry) or for irrigation can reduce runoff volume. The opportunities forvolume reduction through re-use are most significant for high density residentialand commercial land uses with high water use.

Chapter 7 provides quantitative information on the effectiveness of these stormwater sourcecontrol options under various conditions (e.g. rainfall, land use, soil type), and also providesfurther guidance on low impact site design practices and absorbent landscaping.


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Determining What is AchievableEstablishing a rainfall capture target, as shown in Step #3, provides a starting point that isbased on the characteristics of a healthy watershed. The next step is to determine what isachievable and affordable based on assessments of constraints and opportunities in individualcatchments.

Based on these assessments, catchment-specific performance targets and design guidelinesfor achieving these targets can be established. These catchment-specific targets andguidelines will then provide direction for all land development projects within eachcatchment.

The following information is key to assessing opportunities and constraints in any givencatchment:

� Soils Information - Soil conditions govern the feasibility and affordability of usinginfiltration facilities to meet rainfall capture targets. At the watershed planning level,coarse level soils mapping can provide local government staff with the informationneeded to determine where infiltration makes sense, and to evaluate the level ofrunoff volume reduction that could be achieved through infiltration in variouscatchments. This will enable the establishment of catchment-specific performancetargets.

It is also important to evaluate soil conditions at the site level, in order to determinehow much infiltration area is required to meet catchment-specific targets, and toidentify the most suitable infiltration areas within a development site (see the casestudy example on the following page).

� Land Use Information – Land use information will provide local government staffwith guidance regarding where source control options other than infiltration shouldbe considered. In multiple family and commercial land uses, or where opportunitiesfor infiltration are limited, there may be opportunities to achieve significant levels ofrunoff volume reduction by implementing green roofs or rainwater re-use.


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Case Study Example: Design Guidelines for Infiltration FacilitiesSince the majority of new development in the City of Chilliwack are likely to be singlefamily residential, the City’s guidelines for rainfall capture focus on infiltration.

The key design parameter for infiltration facilities is footprint area. Increasing the area ofinfiltration facilities improves their effectiveness at reducing runoff volume, but alsoincreases their cost.

Determining What is Achievable Through InfiltrationSoil conditions govern the feasibility and affordability of using infiltration facilities to meetrainfall capture targets. Figure 6-8 shows that the amount of infiltration area required to meetChilliwack’s rainfall capture target becomes very large where the hydraulic conductivity ofsoils is low.The City’s rainfall capture target is not likely achievable through infiltration in areas wherethe hydraulic conductivity of local soils is less than about 5 mm/hr (typical of soils with highclay content). Also, infiltration is not likely feasible in areas where the regional water table isat or very near the ground surface. Where appropriate, alternative source control strategies(green roofs or rainwater re-use) should be considered in areas where the opportunities forinfiltration are limited.

Chilliwack’s approach allows for flexibility in setting catchment-specific performance targetsthat reflect what is achievable and affordable.

Catchment-Specific Performance TargetsChilliwack has adopted three levels of stormwater planning: watershed, sub-watershed andcatchment. Catchment-specific performance targets will be established through the masterplanning process (at the sub-watershed level) based on a planning-level assessment of soiland groundwater conditions in individual catchments. Having catchment-specific targets willthen provide direction for all land development projects within that catchment.

City of ChilliwackInfiltration Area Required to Achieve Rainfall Capture Target

(per 1000 m2 of Impervious Area Served)

050

100150

200250

300350

400450

500

0 10 20 30 40 50 60 70 80 90 100

Hydraulic Conductivity of Site Specific Soils (mm/hr)

Min

imum

Foo

tprin

t Are

a fo

r In

filtra

tion

Fac

ilitie

s (m

2 )

Soil Types Typical HydraulicConductivity Range

� Sands and gravels > 50 mm/h� Sandy loams 10 – 50 mm/h� Silty loams 5 – 40 mm/h� Clay loams 2 – 6 mm/h� Clays < 2 mm/h

Infiltration Facility Type:Bioretention area with 1 metre of absorbent soiland 300 mm of ponding on surface

Figure 6-8


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Communicating Performance Targets to DevelopersChilliwack’s Design Guidelines for Stormwater Systems (see Chapter 7) include a step-by-step procedure for land developers to follow in order to design infiltration facilities that meetthe City’s rainfall capture performance targets. These Guidelines apply to all landdevelopment projects in catchments where the rainfall capture target is consideredachievable.

Figure 6-8 shows an example design curve for sizing a particular type of facility based on thehydraulic conductivity of site specific soils.

Soils InformationChilliwack has been building a database of the soils data submitted with developmentapplications throughout the City. Using this information, coarse level soils mapping has beenprepared to provide City staff and developers with guidance regarding where infiltrationmakes sense. This soils information will be used to develop catchment-specific performancetargets.

At the site level, developers are required to perform soil investigations and percolation testingto identify the best infiltration areas and to design infiltration facilities.

Infiltration facilities should be sized based on site-specific estimates of saturated hydraulicconductivity. To obtain these estimates, on-site specific percolation tests should beperformed at the location and depth of proposed infiltration facilities, and carried out undersaturated soil conditions.

Developers may consider using areas with the best soil conditions to locate neighbourhoodinfiltration facilities serving multiple dwelling units.

Estimating Hydraulic Conductivity of SoilsThe hydraulic conductivity of soils can initially be estimated through on-site percolationtesting. These estimates can be improved over time by monitoring infiltration facility waterlevels and overflows (see Step #6).

It is also possible to estimate hydraulic conductivity based on soil texture and composition.A good reference is Washington State University’s on-line Soil Texture Triangle(http://www.bsyse.wsu.edu/saxton/soilwater/), which estimates hydraulic conductivity basedon approximate sand and clay content. The typical conductivity ranges shown on Figure 6-8were obtained from this source.

The Importance of Protecting Infiltration AreasWhere infiltration facilities are to be located, it is critical to maintain soils in their natural,undisturbed state and to prevent sedimentation during construction. This requires:

� sediment and erosion control during construction to prevent clogging of rainfallcapture facilities and their underlying soils

� management of constructions sites to prevent disturbance and compaction ofinfiltration areas; infiltration areas should be identified by fencing or other means

Failure to adequately protect infiltration areas during construction will likely result in failureto achieve rainfall capture targets.


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Design Guidelines for Runoff Control (Managing Tier B Events)In order to meet runoff control targets, the combination of source control facilities andcommunity detention facilities should have the capacity to detain the MAR. Increasing thelevel of runoff reduction achieved through source control (i.e. rainfall capture) decreases thestorage volume needed in community detention facilities.

For detention facilities, the operational objective is to replicate the hydrograph of anundeveloped drainage catchment as closely as possible. Therefore, the rate of release fromdetention facilities should approximate the natural streamflow rates that results from Tier Brainfall events (i.e. the target events for runoff control). Ideally, this release rate should beestimated based on streamflow monitoring from undeveloped catchments, as shown in thefollowing case study example.

Case Study Example: Design Criteria for Runoff Control FacilitiesChilliwack has established preliminary detention storage and release criteria to achieve theCity’s runoff control target (i.e. detain rainfall events up to 60 mm per day and release at thenatural interflow rate).

Storage VolumesFor development sites that achieve the City’s rainfall capture target (i.e. capture the first 30mm per day), an additional 300 m3 of detention storage (i.e. 30 mm x 10 m3 per mm) shouldbe provided in community detention facilities.

Developers can reduce the size of detention facilities by increasing the size of infiltrationfacilities. The City’s Design Guidelines for Stormwater Systems (see Chapter 7) provide astep-by-step procedure for designing integrated infiltration and detention systems and allowdevelopers to make trade-offs between storage at the source and community storage.

Similarly, in catchments where the City’s rainfall capture target cannot been achieved due tophysical constraints (high water table, poor soils), more detention storage is required.

Release rate is not subtracted from storage volume criteria, which builds in a safety factor toaccount for back-to-back rainfall events. Performance monitoring may demonstrate that thesafety factor is not needed in future development phases (see Step #6).

Release RatesIn 1999, the City of Chilliwack was proactive in setting up a network of streamflowmonitoring stations, including two in natural forested catchments. This has enabled the Cityto establish the following detention release rate that approximates the natural forestedcondition.

Continued operation of the streamflow monitoring stations in the forested catchments (priorto development occurring in these catchments) will enable validation and refinement of thisrelease rate. Post-development streamflow monitoring will enable the operation of detentionfacilities to be optimized (see Step #6).

Preliminary Release Rate for Detention Facilities in the City of Chilliwack= 1 L/s per hectare (total area tributary to the detention facility)


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Design Guidelines for Flood Risk Management (Managing Tier C Events)

Conveyance of peak flows from extreme storms and minimizing flood risk was the focus oftraditional drainage engineering. While the focus has shifted to managing the completespectrum of rainfall events (i.e. incorporating rainfall capture and runoff control), the floodrisk management function is still an essential component of the overall strategy.

Providing Escape Routes for Extreme StormsFlood risk management at the site level requires a common sense approach to site drainage.The objective is to ensure that the runoff from extreme rainfall events, such as a 100-yearstorm event, can escape to downstream watercourses without posing a threat to property orpublic safety. To achieve this objective, three design conditions must be addressed:

� All rainfall capture and runoff control facilities must include overflow escape routesto allow extreme storms to be routed to downstream watercourses, either as overlandflow or via a storm drainage system (swales, ditches or pipes).

� Sites must be graded to ensure that any overland flow resulting from extreme stormsis dispersed away from areas where flooding problems could otherwise result (e.g.residential properties in low-lying areas).

� The downstream storm drainage system must meet assessment criteria for bothhydraulic and physical adequacy to handle the runoff from upstream developmentareas (refer to adjacent discussion).

Note that managing volume at the site through rainfall capture and runoff control will alsoreduce peak rates of stormwater runoff resulting from extreme storms.

Ensuring that Drainage Installations in Watercourses are Adequately DesignedDrainage system requirements for adequate containment and conveyance of stormwaterrunoff via watercourses are highly site-specific. However, the risk and acceptability of anydrainage facility should be assessed in the context of two basic criteria:

� Hydraulic Adequacy – A comparison of rated capacity versus design flow

� Physical Adequacy – A qualitative judgement regarding physical constraints (e.g.culvert blockage) that could adversely impact hydraulic adequacy

Based on long-term experience, the governing criterion is almost always physical adequacy,with hydraulic adequacy generally being a secondary concern. Assessment of physicaladequacy is a key input for any flood risk analysis.

Drainage problems often occur in small tributaries where stream crossings, such as culvertinstallations, are vulnerable to blockage (i.e. physically inadequate). Flooding may be acommon occurrence at tributary stream crossings even though conventional analysis indicatesthat the conveyance capacity (i.e. hydraulic adequacy) is adequate.

Guiding Design Principle for Stream Crossings: Maintain Waterway OpeningA guiding principle for the design of stream crossings is to preserve or improve the cross-sectional area and gradient of the natural waterway. Clear span bridges are typically betterthan culverts.

A smooth flow condition should be maintained through culvert installations to minimize thedegree of interference with creek processes. If this principle is followed, then the need forpeak flow estimates to design culverts is diminished because it is of incidental interest.Physical acceptability governs.


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Physical Acceptability of Culvert Installations in WatercoursesThe high-risk locations for stormwater system failure are most often at culvert installationsthat are vulnerable to blockage (often on the smaller watercourses). Assessment of physicaladequacy for culvert installations involves a 3-step process:

� Conformance with Design Guidelines (Step #1): Assess the overall conformance withthe nine guidelines for effective culvert design presented below.

Nine Guidelines for Effective Culvert Design

1

2

3

4

5

6

7

8

9

Maintain line and grade of creek channel

Maintain the waterway opening by ‘bridging’ the creek channel

Construct inlet structure to provide direct entry and accelerated velocity

Ensure that culvert can pass trash, small debris and bedload material

Install debris interceptor upstream to provide protection from large debris

Provide scour protection to prevent undermining of the outlet structure

Incorporate provision for an overflow route in the event of a worst-casescenario

Provide equipment access for ease of maintenance (debris removal)

Consider environmental issues, such as fish passage

� Vulnerability to Blockage (Step #2): Assess culvert vulnerability and probability ofculvert failure due to blockage. The potential for blockage reflects the bedload anddebris characteristics of a creek.

� Consequences of Failure (Step #3): Assess the consequences of culvert failure due toblockage (e.g. road failure, damage to downstream properties)

The nine guidelines can be used to qualitatively assess the adequacy of existing facilities aseither poor, fair, good or excellent. The outcome of Step #1 is an overall rating.

The results of Step #2 and Step #3 then determine the acceptability of the overall rating andwhether or not to replace an existing facility.

The level of risk associated with the status quo then determines the need for and timing ofreplacement.

The Importance of Erosion Control for Flood ManagementThe culvert blockages that are often the cause of flooding problems on tributary streams canusually be traced back to two sources:

� erosion and deposition of bedload material

� transport of floatable debris such as branches and brush

Deposition of bedload material also results in the progressive reduction of drainage channelcapacity, which increases flooding risk and can create an ongoing channel maintenanceproblem.

As discussed in Chapter 2, these physical processes are the result of increases in volume andrate of surface runoff. Therefore, providing rainfall capture and runoff control to reduce thevolume and rate of runoff is an important part of flood risk management.


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Flood Management Guidelines for Agricultural AreasA primary flood management objective for agricultural areas is to provide adequate drainageto ensure that the frequency and duration of flooding in agricultural areas does not inhibitproductivity. Meeting the following drainage criteria from the Agri-Food RegionalDevelopment Subsidiary Agreement (ARDSA) will ensure that flood management is adequatefor agriculture:

� Flooding should be limited to a maximum of five days for the 10-year, 5-day winterstorm (November to February).

� Flooding should be limited to a maximum of two days for the 10-year, 2-day growingseason storm (March to October).

� Between storm events, the baseflow in ditches should be maintained at 1.2 m belowthe average ground level to provide free outlet for drains.

Note that these criteria are based on winter storms with a 10-year return period, which aresignificantly larger than a MAR (corresponds roughly to a 2-year return period).

The stormwater management practices required to achieve flood management criteria foragricultural areas will be highly watershed-specific, and should be evaluated as part ofIntegrated Stormwater Management Plans (ISMPs).

It is important to consider agricultural drainage objectives in the context of other objectives.For example, there may be a need to achieve a balance between the third ARDSA criteriondefined above, and a fisheries objective of maintaining adequate low flows in channels toallow for fish passage, since agricultural drainage channels are often used as fish migrationcorridors.

Impacts from Upstream AreasA key stormwater planning consideration is the potential impact that development could haveon downstream agricultural areas (and vice versa). A common stormwater-related problem isthe increase in frequency of flooding of agricultural areas as a result of increased runoff fromupstream development areas. Implementing site design practices that meet rainfall captureand runoff control targets will mitigate this problem to a large extent.

Impacts on Downstream AreasAgricultural areas can also have an impact on downstream urban and suburban land uses.This is often related to water quality impacts associated with agricultural land uses. Specificpractices for managing water quality in agricultural areas (e.g. proper storage of manure) arebeyond the scope of this Guidebook.


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Step #5 – Evaluate Source Control Options ThroughContinuous Simulation Water Balance ModelingThe Importance of Continuous Simulation for Site DesignThe most appropriate site design solutions for achieving rainfall capture targets on any givendevelopment site will depend on site-specific conditions such as soil type, land use type,rainfall and groundwater characteristics.

Continuous simulation modeling provides a tool to evaluate site design options under a fullrange of operating conditions (i.e. the complete rainfall spectrum).

While single event modeling provides an expedient way of establishing capacities and sizesfor the design of conveyance facilities, it does not account for seasonal variation inhydrologic parameters such as antecedent soil moisture and evapotranspiration capacity. Nordoes it account for the frequently occurring small rainfall events (the focus of rainfallcapture). Chapter 7 provides a more detailed discussion on continuous simulation modelingfor stormwater source controls.

Chapter 10 provides a more detailed discussion on the applications of single event andcontinuous simulation modeling in the context of integrated stormwater management plans(ISMPs).

Water Balance ModelingWater Balance modeling using spreadsheets is a cost-effective method to ensure that thedesign of rainfall capture and runoff control facilities:

� meets performance targets for reducing runoff volume and rate� is practical and achievable in the context of local conditions

Water Balance modeling for rainfall capture and runoff control facilities serves severalpurposes:

� Validates preliminary design criteria – Model outputs will provide confidence thatpreliminary design criteria meet (or exceed) performance targets for rainfall captureand runoff control.

� Provides a benchmark for future evaluation – Model outputs will guide theperiodic evaluation of stormwater system performance and facilitate the process ofoptimizing design criteria (see Step #6).

� Provides further design guidance for source control facilities - The performanceof source control options will depend on site-specific conditions such as soilconditions, land use and rainfall characteristics. Water Balance modeling helps withthe selection of appropriate design options.

Case Study Example: Applying Water Balance Modeling to Evaluate theEffectiveness of Stormwater Source Control OptionsThe Water Balance Model (WBM) is a continuous simulation model that has been developedto simulate the hydrologic performance of stormwater source control options (i.e. how wellthey reduce the volume and rate of runoff). This model has evolved through case studyapplications of the Water Balance design approach presented in this Guidebook, including:

� developing design criteria for infiltration facilities in the City of Chilliwack(discussed in Step #4)

� evaluating the potential effectiveness of a broader range of stormwater source controloptions in the Greater Vancouver Regional District (GVRD), including:� absorbent landscaping� infiltration facilities (on lots and along roads)� green roofs� rainwater re-use

Key findings from the GVRD source control evaluation are presented in Chapter 7.


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Step #6 - Optimize Stormwater System Design ThroughAdaptive ManagementThe performance targets and site design criteria presented in Steps #1 through #5 provide astarting point for the design of stormwater systems.

Stormwater system design criteria should be reviewed periodically (e.g. every 3 years), andoptimized based on a detailed performance evaluation. The primary objective of thisevaluation is to reduce stormwater-related costs while still achieving the defined goals andobjectives for protecting downstream property, aquatic habitat and receiving water quality.

Performance Evaluation at the Site LevelMonitoring and evaluating the performance of demonstration projects at the site level is theprimary basis for optimizing the design of stormwater systems. Figure 6-9 shows theindicators that should be monitored to enable a thorough evaluation of stormwater systemperformance.

Monitoring water level and flow in rainfall capture and runoff control facilities provides thebasis for performance evaluation. A continuous record of water level and flow in rainfallcapture and runoff control facilities (including road drainage flows) over an extended timeperiod, combined with continuous rainfall data over the same time period, provides anaccurate picture of how water moves through a stormwater system.

This continuous record will provide answers to key questions related to stormwater systemperformance, such as those shown in the adjacent table.

Framework for Performance Evaluation

For Rainfall Capture Facilities:� What is the frequency and

volume of overflow?� Are targets for runoff volume

reduction being achieved?� How often does water

accumulate?� How fast does water level drop

(i.e. infiltrate) under saturatedsoil conditions?

� What would be the effect ofincreasing/ or decreasinginfiltration area?

� What would be the effect ofdecreasing storage volume?

For Runoff Control Facilities:� What is the frequency and

volume of overflow?� Are targets for runoff rate

control being achieved?� Do detention facilities

empty prior to largerainfall events?

� What would be the effectof decreasing storagevolume?

� Does the outflowhydrograph from detentionfacilities resemble thehydrographs observed atthe streamflow monitoringstations in adjacentundeveloped catchments?

For Road Infiltration/Drainage:� Where does road runoff

go?� How much runoff

discharges to detentionponds? storm sewers?directly to watercourses?

� How much infiltrates?� How fast does road runoff

and overflow from rainfallcapture facilities enter theroad drainage system?

� are the targets for runoffvolume reduction and ratecontrol being achieved?*

* These targets will depend on the road design objectives. Roads may be designed to provide rainfall capture or tobe ‘self-mitigating’ (i.e. provide rainfall capture and runoff control).

Case Study Example: Communicating Performance MonitoringRequirements to Developers

The City of Chilliwack’s Design Guidelines for Stormwater Systems (refer to Chapter 7)include requirements for performance monitoring, which correspond to Figure 6-9.


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Performance Monitoring Requirements

Note:

Indicator OF1 OF2 Road Drainage Streamflow

PerformanceTargets

� Total overflowvolume shouldbe about 10%of total runoffvolume.

� The frequencyof overflowsshould beabout 6 to 8times per year,on average.

� Total overflowvolume shouldbe about 3% ofthe total runoffvolume.

� The frequencyof overflowsshould beabout once peryear, onaverage.

� total flow inthe roaddrainagesystem shouldmeet thevolume andfrequencytargets(3) forOF1 or OF2

� The pre-developmenthydrographshould bemaintained indownstreamwatercourses.

(1) Compound weir outlet structures will enable overflow from rainfall capture facilities and outflow fromrunoff control facilities to be correlated with water levels (WL1 and WL2, respectively). Overflow fromrunoff control facilities (OF2) can be determined by subtracting controlled release (a known parameter)from total outflow.(2) The amount of road runoff that infiltrates can be determined by subtracting FR from total road runoff(and accounting for OF1).(3) If the design objective for roads is to provide rainfall capture, then the targets for OF1 would apply. Ifthe design objective is to make roads ‘self-mitigating’ (i.e. provide rainfall capture and runoff control), thenthe targets for OF2 would apply. Note that storage does not need to be provided in runoff control facilitiesfor self-mitigating roads.

MonitorOverflow(1)

(OF1)

MonitorOutflow(1)

=Controlled Release

at 1 Lps per ha.+

Overflow (OF2)

Rainfall CaptureFacilities (Tier A)

Monitor WaterLevel (WL1)

Runoff ControlFacilities (Tier B)

Monitor WaterLevel (WL2)

Infiltration(Rate of infiltration fromrainfall capture facilitiescan be determined bymonitoring WL1)

MonitorStreamflow and

Turbidity

RainwaterRe-use

+Evapo-

transpiration

Interflow

Monitor RainfallRunoff fromrooftops andparking areas

Site Level Indicators

Catchment Level Indicators

#

#

Runoff fromroads

MonitorFlow(2)

(FR)

RoadInfiltration/Drainage(Tier A)

Note: These overflow targets relate to the typical volume and frequencydistribution of Tier A and Tier B rainfall events.

Figure 6-9


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Deciding Which Facilities to MonitorTo properly evaluate the performance of a demonstration stormwater management system, acomprehensive monitoring program should define the Water Balance of the development siteserved by that system. This means that the monitoring information must answer thefollowing question:

� Where does the rain that falls on the site end up?

Not every rainfall and runoff control facility needs to be monitored, however, it is importantto monitor a representative sample from each component of the stormwater system. Forexample, a comprehensive monitoring program for a residential subdivision may include:

� On-lot rainfall capture monitoring (Tier A) – Monitor water level andoverflow from at least one on-lot rainfall capture facility.

� Road infiltration/drainage monitoring (Tier A) – Monitor the drainage from atleast one section of road, which may include more than one drainage path (e.g.french drains and catch basins).

� Community detention pond monitoring (Tier B) – Monitor water level andoutflow from a detention pond serving the entire subdivision.

The monitoring information from a stormwater system should enable the performance of eachstormwater system component and the performance of the overall system to be evaluatedseparately based on the appropriate performance targets and design objectives.

Testing Conservative AssumptionsTo deal with uncertainty, the preliminary stormwater system design criteria presented inSteps #1 through #5 are based on conservative assumptions:

� Detention storage volumes are conservative because they are based on long-duration rainfall events (24 hr) and do not account for release rate.

� Infiltration facility design criteria are based on conservative modelingassumptions.

Performance monitoring would be expected to confirm that initial assumptions areconservative and provide the certainty needed to reduce the size of facilities installed insubsequent developments. This should translate into cost savings over time.

Customizing Infiltration Criteria for Different ZonesThe rate of infiltration from on-lot or on-road infiltration facilities, and from unlineddetention ponds, depends on soil conditions.

Monitoring the water level in rainfall capture or runoff control facilities will demonstrate howmuch water actually infiltrates and how the infiltration rate varies throughout the year.

This site-specific information can be used to develop customized design criteria for zones thathave similar soil types.


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Performance Evaluation at the Catchment LevelPerformance evaluation at the site level is the primary basis for optimizing the design ofstormwater systems. Performance evaluation at the catchment level is also important toensure that overall objectives for protecting aquatic habitat and receiving water quality arebeing achieved over time, and to improve stormwater management practices. Performanceevaluation at the catchment level may require monitoring of:

� Hydrologic Indicators (e.g. change in rainfall-runoff response). Monitoringrainfall and runoff patterns provides an understanding of the effectiveness ofsource control strategies at maintaining or restoring the catchment’s naturalWater Balance and hydrology.

� Water Quality Indicators (e.g. change in total suspended solids (TSS)).Monitoring changes in TSS provides an indicator of improvements or declines inwater quality. TSS acts as a ‘carrier’ for other pollutants such as heavy metals,and provides a direct measure of stream erosion and sedimentation rates.

� Ecological Indicators (e.g. abundance of benthic invertebrate community).Monitoring the characteristics of benthic invertebrate communities can provide adirect measure of changes in stream health over time.

Hydrologic Performance EvaluationA key performance objective is to maintain, as closely as possible, the characteristics of thenatural hydrograph (i.e. hydrograph of the catchment in its undeveloped state), including:

� total flow volume� peak flow rates� baseflow rates (i.e. interflow)� hydrograph shape

Note that when natural forest cover is removed a certain amount of natural evapo-transpiration capacity is lost. Therefore, an increase in total flow volume is almost alwaysexpected from developed catchments (unless rainwater re-use is implemented). Thisunderscores the importance of land development practices that preserve and/or restore asmuch natural forest cover as possible. The use of green roofs can also limit, though notreplace, the loss of natural evapotranspiration capacity.

Continued streamflow monitoring at the catchment level will answer the following keyperformance evaluation question:

� How well are stormwater management practices at the site level maintaining thecharacteristics of a natural hydrograph as development proceeds within acatchment?

Water Quality Performance EvaluationAnother performance objective is to maintain pre-development water quality. Turbidity andtotal suspended solids (TSS) are key water quality indicators that can be monitored at thecatchment level. Because turbidity can be correlated with TSS, turbidity monitoring could beeffectively integrated with streamflow monitoring.

A water quality baseline should be established by measuring turbidity and TSS prior todevelopment proceeding in a catchment. This will enable future water quality monitoring toanswer the following performance evaluation question:

� How well are stormwater management practices at the site level maintaining thepre-development water quality?

Benthic Monitoring as an Early Warning IndicatorThe Benthic Index of Biological Integrity (B-IBI) is a direct indicator of stream health. Forstreams that are seen as highly valuable (by citizens or environmental agencies), establishinga B-IBI baseline and implementing an ongoing monitoring program would provide an ‘earlywarning’ of stream degradation, and signal the need for action.

A Look AheadChapter 10 elaborates on environmental monitoring techniques that can be used to measuresuccess at the catchment scale. This includes a discussion of the suite of tools that comprise acomprehensive approach, and an overview of the appropriate scale on which to use them.The key message is that this suite of indicators accurately represents the environmental stateof both the surface drainage function and the ecological function of receiving waters and cantherefore be used to evaluate and optimize stormwater management strategies over time.

Chapter Seven

7.1 Overview of Site Design Strategies for Achieving Performance Targets

7.2 Low Impact Development Practices� Reducing Impervious Area� Stormwater Source Control – A Key Element of Site Design� Consistency with Other Low Impact Development Objectives� Preserving Significant Natural Features

7.3 Stormwater Source Control Practices� The Role of Source Control� Guidance for Selecting Appropriate Source Controls� Modeling the Effectiveness of Source Controls� Integrating Source Controls into ISMPs� Evaluating the Cost of Source Controls� Ensuring the Long-Term Performance of Source Controls� Operation and Maintenance Implications� Water Quality Benefits of Source Control

7.4 Type 1 Source Control - Absorbent Landscaping� The Importance of Surface Soil and Vegetation� Absorbent Soil and Vegetation Characteristics� Absorbent Soil Depth� The Importance of Forests� The Benefits of Absorbent Landscaping for Different Rainfall Conditions� Benefits of Absorbent Landscaping for Different Land Use Types� Cost Implications of Absorbent Landscaping� Maintenance Tips for Absorbent Landscaping� Rehabilitation of Disturbed Soil

Site Design Solutions forAchieving Performance Targets



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7.5 Type 2 Source Control - Infiltration Facilities� The Importance of Disconnecting Impervious Surfaces� Different Types of Infiltration Facilities� Factors that Affect the Performance of Infiltration Facilities� The Effectiveness of Infiltration under Different Rainfall Conditions� Selecting Infiltration Facility Depth� The Importance of Infiltration Area and Soil Type� Determining What is Feasible and Affordable� Infiltration Facilities for Land Uses with High Impervious Coverage� Performance of Infiltration Facilities for a Range of Land Use Types� Performance of Infiltration Facilities on Roads� Achievable Level of Runoff Volume Reduction for Different Land Use Types� Creating Hard Surfaces that Infiltrate� Applying Combination of Infiltration Strategies� Cost Implications of Infiltration Facilities� Design and Construction Tips for Infiltration Facilities� Operation and Maintenance Tips for Infiltration Facilities

7.6 Type 3 Source Control - Green Roofs� The Effectiveness of Green Roofs under Different Rainfall Conditions� The Importance of Green Roof Soil Depth� Benefits of Green Roofs for Different Land Uses� Cost Implications of Green Roofs� Design and Construction Tips for Green Roofs� Operation and Maintenance Tips for Green Roofs

7.7 Type 4 Source Control - Rainwater Re-use� Benefits of Rainwater Re-use for Different Land Uses� The Effectiveness of Rainwater Re-use under Different Rainfall Conditions� Selecting an Appropriate Storage Volume� Cost Implications of Rainwater Re-use� Design and Construction Tips for Rainwater Re-use� Operation and Maintenance Tips for Rainwater Re-use

7.8 Applying Source Controls to Mitigate Extreme Cloudbursts

7.9 Communicating Performance Targets to Developers� Case Study Example: Design Guidelines for Developers


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7.1 Overview of Site Design Strategies for AchievingPerformance TargetsChapter 6 showed how to establish performance targets. This chapter presents site designstrategies for achieving performance targets, including:

� Low Impact Development Practices that:

� minimize the creation of impervious cover (i.e. reduce total impervious area(TIA)) and other land cover changes that are detrimental to downstreamwatercourses, such as clearing of natural vegetation and compaction of soils.

� preserve natural features that are key to maintaining healthy aquatic ecosystems,such as riparian forests and wetlands.

� Stormwater Source Control Practices that capture rainfall at the source (on buildinglots, road right-of-ways, or in neighbourhood facilities) and return it to naturalhydrologic pathways - infiltration and evapotranspiration - or re-use it at the source.Source controls create hydraulic disconnects that reduce effective impervious area (EIA).

Catchment-specific performance targets for rainfall capture and runoff control may beachieved at the site level through some combination of these strategies.

Section 7.2 discusses low impact site design practices, and Sections 7.3 through 7.8 provideguidance for selecting appropriate stormwater source control options.

Section 7.9 shows how to communicate performance targets and related design guidelines todevelopers so that they can be applied at the site level.


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7.2 Low Impact Development Practices

Reducing Total Impervious AreaRunoff from impervious surfaces is the primary cause of drainage-related problems such asstream degradation and flooding risk. Limiting impervious coverage can reduce runoffvolume and partially mitigate these problems.

At the Land Use Planning LevelImpervious coverage can be controlled at the land use planning level by controlling wherecertain land use types are permitted. Limiting the amount of development, or controlling thetype of development, in catchments where local and downstream ecosystem values could benegatively impacted, can be a science-based strategy to support stormwater managementgoals.

However, stormwater is just one of many factors that need to be considered when makingland use decisions.

At the Site Design LevelThere are a number of site design practices that can reduce impervious coverage for a widerange of land uses, including:

� Reducing Road Widths – Paved roadways are often larger than they need to be.Reducing road width not only reduces impervious area, but also reduces motorvehicle speeds, improves pedestrians and bicycle safety, reduces infrastructure costsand allows more of the paved surface to be shaded by overarching tree canopy.

� Reducing Building Footprints – Building footprints can be reduced (thus reducingrooftop area) without compromising floor area by relaxing building heightlimitations. Taller, more slender building forms provide greater flexibility todevelop building layouts that preserve naturally vegetated areas and provide spacefor infiltration facilities. This also has important implications for integrating sourcecontrol into site design, as discussed in Section 7.5.

� Reducing Parking Standards - Reducing parking standards reduces the amount ofspace devoted to parking (driveways, parking lots and parkades). In compact and/or

high density communities where dwelling units are within walking distance to transitand services, parking standards may be reduced to 1.3 or even as low as 1 space perdwelling unit. There are other factors that could reduce the need for parking,including a high proportion of low income housing units, the implementation oftransportation demand management strategies, and high parking costs. Reducingparking standards not only reduces impervious area, but also reduces parking-relateddevelopment cost, and facilitates the provision of affordable housing.

� Limiting the Amount of Surface Parking – The more parking provided within thebuilding envelope (e.g. underneath other land uses), the less additional lot area willbe needed for parking. For parking outside the building envelope, surface parkingtypically creates far more impervious coverage than parkades. There is also greateropportunity to mitigate the runoff from parkades using green roofs or rainwater re-use (see Sections 7.6 and 7.7). Generally, underground parking only occurs whereland economics favour residential or commercial development over surface parking.

� Building Compact Communities – Building compact communities enables morenatural area to be preserved, thus reducing impervious coverage at the watershedscale. In a compact community pattern, there can be up to 75% less roadwaypavement per dwelling unit. The need for parking is also reduced in compactcommunities, as discussed previously.

Site design practices that reduce total impervious areas also reduce clearing of naturalvegetation and the compaction of natural soils (total site disturbance is reduced).

Reducing Impervious Area Improves Source Control EffectivenessReducing impervious coverage on lots and roads can improve the effectiveness ofstormwater source controls, particularly infiltration facilities. Less impervious coverage onroads and building lots means that:

� less runoff becomes concentrated into infiltration facilities� more space is available to locate infiltration facilities

This can significantly improve the effectiveness of infiltration facilities, as discussed inSection 7.5.


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Stormwater Source Control – A Key Element of Site DesignImplementing low impact site design practices that reduce impervious coverage is notenough to protect downstream watercourses and prevent drainage-related problems. Evenlow levels of impervious coverage can cause significant stormwater-related impacts. Forexample, the volume of runoff from low-density single family land uses far exceeds thetarget condition for Water Balance management (i.e. the 10% runoff volume target).

Source controls are needed to further reduce runoff from impervious surfaces ondevelopment parcels (rooftops, driveways, parking lots) and roads (paved roadway andsidewalks).

Consistency with Other Low Impact Development ObjectivesSite design practices that achieve stormwater objectives (reducing impervious area, forestclearing and soil compaction) are highly compatible with other low impact developmentobjectives, including:

� Compact communities and cluster development that encourage walking, cycling andtransit use

� Smaller streets that are more pedestrian and cyclist-oriented

� Continuous riparian corridors and open space systems (greenways)

� Preservation of environmentally significant areas

� Tree retention

� Community parks and recreation areas

� Construction practices that minimize soil and vegetation disturbance

� Lower expenditures on infrastructure


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Preserving Significant Natural FeaturesPreserving natural vegetation and soils in their undisturbed state is key to minimizingchanges in the natural Water Balance (i.e. loss of evapotranspiration and infiltrationcapacity). There are certain natural features that are especially important for maintaining thehealth of aquatic ecosystems, including riparian forests, wetlands, natural infiltration areasand floodplains. These features can also have significant benefits in terms of reducing floodrisk.

A key component of an integrated strategy to manage stream health and flood risk is toidentify significant key natural features at a watershed scale, and protect these featuresthrough growth management, land use planning, and development policies and regulations.

Significant natural features should also be identified at the site design level, and preservedthrough creative site design practices that integrate significant natural features withcommunity open spaces.

Riparian ForestsAs discussed in Chapter 2, riparian forests are key to maintaining the health of aquaticecosystems. Preserving riparian forests enables overland flow to infiltrate and directly feedstream baseflow, thus helping to maintain the natural Water Balance.

WetlandsWetlands play a key role in maintaining natural Water Balance and hydrology. They retainlarge volumes of water, and promote recharge of the interflow zone and evapotranspirationfrom wetland vegetation. The vegetation in wetlands also improves water quality byremoving sediments, nutrients and other contaminants such as heavy metals. Wetlands aretypically very productive ecosystems that provide high quality habitat for waterfowl, fish andother wildlife. Constructed wetlands can be used to manage runoff from developed areas.

Natural Infiltration AreasNatural areas where large volumes of rainfall infiltrate (e.g. natural depressions with highlypermeable soils) are key to maintaining the natural Water Balance and should be preserved.Natural infiltration areas that directly feed stream baseflow (e.g. riparian corridors) are

particularly important. These areas may also be used to infiltrate runoff from impervioussurfaces.

FloodplainsNatural floodplains provide the space for streams and rivers to expand during periods of highrainfall and/or snowmelt. Floodplains provide natural flood control by dissipating the energyof high peak flows. Confining watercourses using flood protection structures such as dykesprevents this natural energy dissipation, and increases the risk of downstream flooding.

The periodic flooding of floodplain areas is also key to maintaining important ecosystems,including riparian forests and wetlands.

The hydrologic functions of natural floodplains can be preserved by limiting development, orby promoting ‘flood-friendly’ land uses (e.g. types of agriculture that can support periodicflooding, buildings that are flood-proofed) in floodplain areas.


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7.3 Stormwater Source Control Practices

The Role of Source ControlStormwater source control practices can play a key role in achieving performance targets forrainfall capture, runoff control and flood risk management.

The primary objective of source control is to reduce runoff volume (i.e. provide rainfallcapture) by managing the Water Balance at the site level. Source control can also havesignificant benefits in terms of reducing runoff rates (i.e. provide runoff control and floodrisk management).

Source controls can be very effective at reducing runoff volumes and at reducing peak runoffrates from relatively large storms (e.g. 5-year storms) or from very intense short durationstorms (e.g. 100-year cloudburst). However, the ability of source controls to reduce peakrunoff rates from very large, long duration storms (e.g. a 100-year winter storm) is limited.Even with source controls, stormwater systems must be designed to safely convey theseextreme events.

The Need for Information on Source Control EffectivenessIn order to select appropriate source control options to achieve catchment-specificperformance targets, there is a need for information on how well different types of sourcecontrols perform under different conditions (e.g. land use types, soil and rainfall conditions).

There is a lack of scientifically defensible data on the long-term effectiveness and benefits ofdifferent types of stormwater source controls. To bridge this information gap, in the GreaterVancouver Regional District (GVRD) commissioned a report titled Effectiveness ofStormwater Source Controls (2002) to assess the potential effectiveness of various sourcecontrol options (as measured by their ability to reduce runoff volume and peak rate).

The GVRD report provides a quantitative reference on the effectiveness of the followingcategories of stormwater source controls:

� Type 1 - Absorbent Landscaping - refer to Section 7.4� Type 2 - Infiltration Facilities (on lots and along roads) - refer to Section 7.5� Type 3 - Green Roofs - refer to Section 7.6� Type 4 - Rainwater Re-use - refer to Section 7.7

Guidance for Selecting Appropriate Source ControlsSections 7.4 to 7.7 present key information from the GVRD report to show how thehydrologic performance of each source control category (i.e. their ability to reduce thevolume and rate of runoff) varies depending on land use type, soil conditions, rainfallcharacteristics and source control design.

For each source control category, these sections also provide design guidance, discuss costimplications and review operation and maintenance requirements.

The information provided in Sections 7.4 to 7.7 is intended to help local governments:

� identify opportunities to manage stream health and/or stormwater infrastructure byapplying various types of stormwater source controls

� determine what can realistically be achieved through the application of sourcecontrols

� determine which source control options are worth pursuing, and

� estimate the likely return on investment

This provides a starting point for integrating stormwater source control strategies into:

� long-range land use and infrastructure planning decisions

� the design of stormwater systems at the site level

The most appropriate source control options and source control design features for any givendevelopment or re-development site will depend on site-specific conditions.

The selection of source controls to meet catchment-specific performance targets should beflexible to allow for innovation. Local government staff, consulting professionals, ordevelopers that select source control options should consider the need for these options, siteconstraints to their use, expected performance and benefits, maintenance considerations andcosts implications (both positive and negative).

This chapter helps evaluate these factors. For more detailed information on the effectivenessof stormwater source controls refer to the GVRD report.


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Modeling the Effectiveness of Source ControlsThe commonly used hydrologic modeling applications were developed when flow-basedthinking dominated stormwater management and surface water modeling. Therefore, noneof these models are well suited for modeling Water Balance volumes at the site level.

The Water Balance Model (WBM), introduced in Chapter 6, was used to simulate theperformance of source controls under a range of conditions.

Overview of the Water Balance ModelThe WBM provides a continuous simulation of the runoff from a development (or re-development) area, or from a watershed (or sub-catchment) with multiple land uses, giventhe following inputs:

� Continuous rainfall data (time increment of one hour or less) and evapo-transpiration data (daily) over a long period of record (at least a year). Historicrainfall data can be modified to create climate change scenarios.

� Site design parameters for each land use type being modeled (e.g. road width,rooftop coverage, surface parking coverage, population density).

� Source control information for each land use type, including:� extent of source control application (e.g. % of road and % of building lots with a

certain types of source controls)� source control design parameters (e.g. area and depth of infiltration facilities,

soil depth for green roofs or absorbent landscaping, volume of rainwater re-usecisterns)

� Soils information, including:� surface soil parameters (e.g. maximum water content, vegetation rooting depth)� sub-surface soil parameters (e.g. saturated hydraulic conductivity)

Scenario ModelingThe WBM was used to generate a series of scenarios that demonstrate how a range of factors(e.g. rainfall, land use type, soil conditions) affect the hydrologic performance of the varioussource control categories.

The source control modeling was based on the best available knowledge of source controlperformance, but has not been calibrated with measured hydrologic performance data.Performance monitoring from source control demonstration projects will improveunderstanding of how well source controls can reduce runoff under a variety of conditions,and provide the data needed to calibrate the source control models.

The source control scenarios presented in this chapter are examples, and do not reflect thecomplete range of available source control options. The examples are intended to provide astarting point for evaluating the potential for source control application, and should not limitinnovation in applying combinations and types of source controls.

Chapter 8 presents the results of scenario modeling for case study watersheds to demonstratewhat is achievable at the watershed scale through the application of source controls.


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Integrating Source Controls into ISMPsSource controls are applied at the site level, but must be implemented in the context of anIntegrated Stormwater Management Plan (ISMP). At the planning level it is important to:

� Identify stormwater related issues� significant resources to be protected and/or restored� drainage problems, such as high flooding risk

� Characterize development pressures that could affect aquatic ecosystem valuesor drainage system performance� are there plans for new development in existing natural areas?� are there older development areas where re-development is imminent?

� Evaluate the opportunities for implementing stormwater source controls to:� avoid further stream degradation� avoid worsening of drainage problems� improve water quality� restore watershed health over time

Performance targets, such as the 10% runoff volume target, provide a reference point basedon the characteristics of a healthy watershed. The ISMP process will determine what isachievable and affordable in the context of each individual watershed.

Chapter 8 presents case study examples that show how watershed restoration could beachieved over a 50-year timeline through the application of source controls.

Evaluating the Cost of Source ControlsThis chapter discusses cost implications of each source control category and provides order-of-magnitude cost estimates. Detailed cost estimates can only be obtained based on thecharacteristics of each individual development site.

Site-specific costs should be evaluated relative to the potential benefits gained, in terms ofprotecting or improving watershed health and/or in terms of flood risk management. Theinformation in this chapter helps evaluate the benefits of using source control options.

Cost estimates can be misleading if they are not considered in the context of the overalldevelopment process. For example, there may be excavation costs associated with theconstruction of an infiltration facility on a particular lot, but much of this cost may beincurred through the site grading process (even without infiltration).

It is also important to consider the potential cost savings of source controls. For example,applying infiltration facilities may reduce the cost of storm sewer pipes needed for a newdevelopment project, avoid the need for ongoing maintenance of eroded channels, or avoidthe need for drainage infrastructure upgrades.


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Ensuring the Long-Term Performance of Source ControlsSource control facilities typically require ongoing maintenance to ensure that they continueto function effectively over the long term. While this report discusses operation andmaintenance requirements and costs for each source control category, there is a need forfurther research to better define the:

� operation and maintenance practices required to maintain source controlperformance over the long term

� cost of these operation and maintenance practices

To address these research needs and provide further guidance on how maintain the long-termperformance of source controls, it is important to continue monitoring the performance ofsource control demonstration projects over long periods of time and to keep accurate recordsof ongoing operation and maintenance practices.

Operation and Maintenance ImplicationsNew source control practices raise concerns about associated operations, maintenance andliability issues. It is important during any adoption of new design standards to involveoperations and maintenance personnel, and to use their creative and practical talents toanticipate and solve these issues.

Demonstration projects are an excellent way to solve real operations and maintenanceproblems, and to allay false fears.

Certain types of source control facilities may be operated and maintained by localgovernment staff (e.g. infiltration facilities within road right-of-ways). However, manysource control facilities are likely to be on private property (e.g. on-lot infiltration facilities,re-use facilities or green roofs). Responsibility for maintaining these facilities shifts toindividual landowners or strata corporations, which places a greater reliance on theconscientiousness of individuals.

An on-lot stormwater system is similar to an on-lot septic sewage system, in that ownersmust be given basic information about operation and maintenance requirements.

There are potential liability issues related to operation and maintenance responsibility (e.g.who is responsible in the event of a failure?). Local governments should resolve these issues

in collaboration with landowners and the development community. There are parallel issuesrelating to water supply and sanitary sewer systems (e.g. sewer cross connections) that localgovernments have been dealing with for years and could use as precedents.

Education of local government staff, developers and the general public regarding the need forsource controls, as well as their long-term operation and maintenance requirements, isessential to the successful implementation of stormwater source controls.

Section 8 provides further discussion and guidance on how to facilitate the changes instandard practice that are needed to promote the widespread implementation of sourcecontrols.

Water Quality Benefits of Source ControlStormwater source controls capture the first flush of pollutants that wash off fromimpervious surfaces. This is particularly important for roads and parking areas becausepollutants from motor vehicles and road maintenance can accumulate on these surfaces.

Infiltration facilities are particularly beneficial in terms of improving water quality at thesource. Absorption of stormwater runoff in the shallow soil zone filters out sediments andmany pollutants, thus improving downstream water quality.

This chapter focuses on the effectiveness of source controls at reducing runoff volume andrate, because this information enables source control to be evaluated relative to performancetargets for rainfall capture and runoff control. Further research is needed to provide similarquantitative modeling of the effectiveness of source controls for improving groundwater andsurface water quality.

This research should start with a good understanding of the source of water quality problems(e.g. runoff from roadways, lawns and agriculture areas). This understanding will enable theselection of appropriate water quality indicators and the development of an appropriate waterquality model.

As a parallel example, the evaluation of hydrologic effectiveness presented in this reportstarted with a good understanding of the source of water quantity problems (i.e. an increasein the volume and rate of runoff). This understanding led to selection of appropriatehydrologic performance indicators and development of the Water Balance Model.


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7.4 Type 1 Source Control - Absorbent Landscaping

The Importance of Surface Soil and VegetationSurface soil structure plays a fundamental role in stormwater management. Minimizingsurface soil disturbance and using absorbent landscaping can significantly reduce the volumeand rate of runoff from developed areas.

In a natural condition, surface soil layers are highly permeable. Surface plants provide alayer of organic matter which populations of earthworms and microbes stir and mix into thesoil. This soil ecosystem provides high infiltration rates and a basis for interflow thatsupports the baseflow needs of aquatic ecosystems.

In an urbanized condition, it is common practice to remove the surface soil layers, to regradeand heavily compact the site, and then to replace only a thin layer (often 50mm or less) ofimported topsoil. This practice creates a surface condition that results in significant amountof runoff from lawn and landscape areas.

Absorbent Soil and Vegetation CharacteristicsVegetation and organic matter improve soil structure and contribute to macroporedevelopment. This is essential for promoting and maintaining infiltration and evapo-transpiration capacity. To optimize infiltration, the surface absorbent soil layer should havehigh organic content (about 10 to 25%). Surface vegetation should be either herbaceous witha thickly matted rooting zone (shrubs or grass), deciduous trees (high leaf density is best), orevergreens.

A range of soil and vegetation characteristics is acceptable depending on whether the area isto be covered by lawn, shrubs or trees. The soils required by the BC Landscape Standard formedium or better landscape will provide the required hydrologic characteristics. Often thisstandard can be achieved by adding organic matter to existing top soils on a residential site.

Figure 7-1 shows the mixing of soil and organic matter to create a good landscape soil.

A range of acceptable absorbent soil compositions are shown in Section 7.9.

Figure 7-1 Creation of Landscape Soil


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Absorbent Soil DepthFigure 7-2 shows that runoff from landscaped areas can be virtually eliminated by providinga 300 mm layer of landscaped absorbent soil, even under very wet conditions where thehydraulic conductivity of the underlying soil is low.

The Figure assumes that the rooting zone of the surface vegetation extends to the depth ofthe absorbent soil layer, and that absorbent landscaping covers all undeveloped areas.

The Importance of ForestsForests are the most effective form of absorbent landscaping. Since trees typically have verydeep rooting zones (often in the range of 2 metres), there is virtually no surface runoff fromforested areas. Tree canopies that shade impervious surfaces (e.g. roadways) can reduce therunoff from these surfaces by intercepting rainfall.

Preserving and/or restoring as much forested area as possible through implementation of anurban forestry strategy is an effective way to reduce runoff volumes and rates.

The thick layers of absorbent soil in forested areas typically have the capacity to retain andinfiltrate large volumes of runoff (in addition to direct rainfall). Dispersing runoff fromrooftops or paved surfaces over forested areas can be an effective infiltration strategy, asdiscussed in Section 7.5.

Effect of Soil Depth on Performance of Absorbent Landscaping

Single Family Residential Area (50% impervious coverage)North Surrey Rainfall (wet year, 1733 mm annual rainfall)

Poor Soils (hydraulic conductivity of 2.5 mm/h)

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Figure 7-2


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The Benefits of Absorbent Landscaping for Different Rainfall ConditionsFigure 7-3 shows that absorbent landscaping is most beneficial for high rainfall locations.This is because increased rainfall typically leads to greater volumes of runoff from disturbedsoil, but not from absorbent landscaping.

Absorbent landscaping (300 mm soil depth or more) can virtually eliminate surface runofffrom undeveloped areas, even in the wettest conditions. This has significant benefits interms of reducing peak runoff rates from extreme rainfall events, as shown on the followingpage.

Effect of Rainfall on Benefits of Absorbent Landscaping

single family residential area (50% impervious coverage)

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North Surrey(wet year, 1999)

White Rock(dry year, 2000)

Burnaby Mountain (wet year, 1999)

Figure 7-3


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Benefits of Absorbent Landscaping for Different Land Use TypesThe benefits of absorbent landscaping are more significant for land uses with lower levels ofimpervious site coverage and higher proportions of undeveloped area (e.g. single familyresidential), as shown in Figures 7-4 and 7-5.

These figures show the simulated runoff volumes and peak runoff rates during a very wetyear (1999) in North Surrey. A total of 1733 mm of rainfall fell during this year, and themost extreme rainfall event was a long duration, wet weather storm with a 5-year returnperiod.

Figure 7-4 shows that absorbent landscaping is particularly beneficial in terms of reducingpeak runoff rates. During large rainfall events (e.g. a 5-year storm), disturbed soil cangenerate nearly as much runoff as impervious surfaces, whereas an absorbent soil layer (300mm depth) can continue to absorb rainfall. Therefore, absorbent soil can significantly reducepeak runoff rates from large storms, especially for land uses with large amounts ofundeveloped space.

Benefits of Absorbent Landscaping(Peak Runoff Rate Reduction)

North Surrey Rainfall (wet year, 1999)

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er h

ecta

re)



single familymultiple family

commercial

Benefits of Absorbent Landscaping(Runoff Volume Reduction)


0

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20 30 40 50 60 70 80 90 100

% of Land Covered by Impervious Surfaces

Run

off V

olum

e (%

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otal

rain

fall)



single familymultiple family

commercial

Figure 7-4

Figure 7-5


MAY 2002

7-13

Cost Implications of Absorbent LandscapingThe costs of absorbent landscaping are highly variable and depend on site-specific conditionssuch as vegetation type. This reflects the customized nature of individual site landscapingplans.

Typical costs for absorbent landscaping range from about $25 - $70 per m2. In the lowercost ranges, the absorbent soil depth would be about 150 mm, with turf cover and some trees.In the upper ranges, soil depth would be about 450mm, with shrubs or groundcover andtrees.

Maintenance Tips for Absorbent Landscaping� Maintaining the absorbency of soils is an advantage both to turf and plant health and

to stormwater management. Normal landscape maintenance of absorbent soils willgenerally produce an absorbent landscape surface.

� In shrub beds, regular application of bark mulch, natural leaf drop or other organicinputs will keep burrowing insect populations high and maintain soil permeability.

� In lawn areas, use of proper sandy topsoil will avoid compaction problems. Aeratingtechniques can assist air and water exchange in locally compacted areas.

� Bare soils should not be left uncovered (e.g. during construction) because rainfallimpact can create a relatively impermeable surface crust, even in sandy soils.

� Dry season watering of plants is essential, especially when plants are first becomingestablished.

� Maintenance requirements (and costs) are typically highest in the first year whenplants may require more watering, weeding and some replacement.

Rehabilitation of Disturbed SoilThere are a number of ways to convert a disturbed surface soil layer into absorbent soil thathas good hydrologic properties, including:

� Mixing in organic content (e.g. compost); this is the most effective soil rehabilitationtechnique

� Mechanical tilling or scarifying of the surface soil� Soil aeration, which requires specialized equipment

Immediate replanting of the surface soil layer is an essential part of any soil rehabilitationproject.


MAY 2002

7-14

7.5 Type 2 Source Control - Infiltration Facilities

The Importance of Disconnecting Impervious SurfacesDirect runoff from impervious surfaces is the primary cause of drainage-related problems(e.g. stream degradation, flooding risk). This direct runoff can be eliminated to a large extentby infiltrating runoff from impervious surfaces on development parcels (rooftops, driveways,parking lots) and roads (paved roadways and sidewalks).

Figure 7-6a and 7-6b show the runoff volume and rate reduction benefits that can beachieved in one of the wettest parts of the province (North Vancouver) during a very wetyear (2355 mm of annual rainfall) by disconnecting impervious surfaces. These figuresshow that the benefits vary significantly depending on the type of surface and the amount ofspace available to infiltrate runoff (discussed further on the following pages).

Simple DisconnectionsThere is very little benefit gained by impervious surface disconnection if the runoff is simplydispersed over an area with disturbed surface soil.

Dispersing runoff over an area with absorbent landscaping can result in significant runoffvolume reduction, even if the underlying soils have poor hydraulic conductivity. However,this is not likely to reduce peak runoff rates resulting from large, long duration rainfall events(e.g. a 5-year winter storm). Concentrating runoff from an impervious surface area onto asmaller area of absorbent landscape causes the surface soil to become saturated duringprolonged rainfall. There must be an adequate collection and conveyance system (e.g. lawnbasins) to ensure that runoff from saturated soils does not cause water damage, nuisanceproblems, or inconvenience to the public.

The most significant reduction in runoff volume and peak rates can be achieved bydispersing runoff over a forested area. The rooting depth of trees provides significant storagecapacity to retain runoff for extended periods of time and allow it to seep into the ground.

Infiltration FacilitiesThe hydrologic function of a forested infiltration area can be approximated using infiltrationfacilities (e.g. bioretention areas) that are designed to retain runoff and provide time for it toinfiltrate. Different types of infiltration facilities are discussed on the following page.

Benefits of Impervious Surface Disconnection (Runoff Volume Reduction)

Single Family Lot (50% lot coverage)North Vancouver Rainfall (wet year, 1999)

Medium Soils (hydraulic conductivity of 13 mm/h)

0102030405060708090

100

0 5 10 15 20 25

% of lot used for infiltration

Volu

me

of R

unof

f (%

of t

otal

rain

fall )

Disturbed Soil

Absorbent Landscaping(300 mm rooting depth)

Forested (2 m rootingdepth)

Bioretention Area (150mm ponding on top of1 m absorbent soil

No Disconnection

Type of Infiltration Space

Benefits of Impervious Surface Disconnection (Runoff Rate Reduction) Single Family Lot (50% lot coverage),

North Vancouver Rainfall (wet year, 1999)Medium Soils (hydraulic conductivity of 13 mm/h)

05

1015202530354045

0 5 10 15 20 25

% of lot used for infiltrationPe

ak R

unof

f Rat

e fr

om 5

-yr R

ainf

all E

vent

(L

/s p

er h

ecta

re)

Disturbed Soil

Absorbent Landscaping(300 mm rooting depth)

Forested (2 m rootingdepth)

Bioretention Area (150mm ponding on top of 1m absorbent soil)

No Disconnection

Type of Infiltration Space

Figure 7-6a

Figure 7-6b

Dashed lines show runoff reduction for absorbent landscape andbioretention areas underlain by poor soils (hydraulic conductivity of 2.5)

Dashed line shows runoff reduction for bioretention areas underlain by poorsoils (hydraulic conductivity of 2.5 mm/h)


MAY 2002

7-15

Different Types of Infiltration FacilitiesThe storage capacity needed to retain impervious surface runoff and allow it to infiltrate canbe provided:

� in the void space of absorbent soil, sand or gravel layers� on the ground surface (i.e. ponding)� in infiltration chambers (see Figures 7-7a and 7-7b)� in storage structures, such as cisterns; runoff stored in structures must eventually be

released to an infiltration area

Note that the amount of area provided for infiltration is a more important design parameterthan storage volume.

There are two general categories of infiltration facilities:

� Surface Facilities – Runoff is stored in a layer of absorbent soil, sand or gravel, and/oron the ground surface in a ponding area. Surface facilities can be aestheticallylandscaped and integrated into the design of open spaces (often called bioretentionfacilities or rain gardens). Figure 7-8a shows an example of a bioretention facility in theform of a terraced landscape feature on a hillside. Figure 7-8b shows an example ofparking lot runoff draining to linear bioretention areas (landscaped islands in the parkinglot). Bioretention can also be applied at the neighbourhood scale (e.g. constructedwetlands serving multiple dwelling units).

Surfaces facilities can also be infiltration trenches, which store runoff in a layer of cleangravel or stone (see Figure 7-9).

� Sub-surface Facilities – Runoff is stored in sub-surface layers of gravel, sand or drainrock and/or in infiltration chambers (e.g. inverted plastic half pipes). Absorbentlandscaping can be installed over the surface, and with proper engineering, pavement andlight vehicle traffic may be allowed on the surface (e.g. a soakaway pit under adriveway).

Note that infiltration facilities can also be a combination of the two types described above.For example, infiltration swales along roads (see Figure 7-10) may consist of an absorbentsoil layer (surface swale) on top of a sub-surface infiltration trench (gravel filled soakaway).

Design, construction, and operation and maintenance tips for different types of infiltrationfacilities are provided later in this section.

The Need for Escape RoutesAll infiltration facilities must have overflow pipes or channels to ensure that runoff fromextreme storms can escape to downstream watercourses without posing a threat to propertyor public safety. Infiltration facilities along roads (e.g. swales and infiltration trenches) mustalso be designed to convey extreme storms from the development areas they serve (asconventional storm sewers do).

Figure 7-7b

Figure 7-7aInfiltration Chamber

Figure 7-7b


MAY 2002

7-16

Figure 7-8a Bioretention Landscaping Feature

Figure 7-10 Infiltration Swale Along Roadway

Figure 7-8b Bioretention for a Parking Lot

Figure 7-9 Infiltration Trench


MAY 2002

7-17

Factors that Affect the Performance of Infiltration FacilitiesThe hydrologic effectiveness of infiltration facilities (i.e. amount of reduction in runoffvolume and rate) varies depending on the following factors:

� Land Use Type – Infiltration is more challenging for land uses with higher levels ofimpervious surface coverage (e.g. commercial or high-density residential uses). Onhigh coverage land uses there is more surface runoff (thus concentrating more waterinto infiltration facilities), and less space available to locate infiltration facilities.

� Soil Type – The maximum rate at which water can exfiltrate from infiltrationfacilities is controlled by the hydraulic conductivity of soils.

� Amount of Area Provided for Infiltration – Footprint area is the most important designparameter for infiltration facilities. Increasing infiltration area reduces runoffvolume and rate by:� dispersing runoff over a larger area, and thus reducing the concentration of

runoff (governed by the ratio of impervious surface to infiltration area)� increasing the rate at which this runoff can exfiltrate

� Rainfall Characteristics – The effectiveness of infiltration facilities typicallydecreases as rainfall increases. This is because more rainfall results in more runoffto be concentrated into infiltration facilities, which leads to more overflow (i.e.greater volumes and rates of runoff).

� Depth and Type of Infiltration Facility – Increasing the depth and/or void space forstorage in an infiltration facility increases the retention storage capacity, thusdecreasing the amount of overflow (i.e. runoff). In general, infiltration area is amore important parameter than depth.

� Depth to Groundwater – In order for infiltration facilities to be effective, the bottomof the facility must be a reasonable depth (at least 0.5 m) above the groundwatertable. Infiltration facilities are not appropriate in areas where the water table is at ornear the ground surface

The graphs presented on the following pages illustrate how these factors affect theperformance of infiltration facilities.


MAY 2002

7-18

The Effectiveness of Infiltration under Different Rainfall ConditionsFigure 7-11 illustrates how the performance of infiltration facilities (in terms of runoffvolume reduction) decreases as total annual rainfall increases.

More infiltration area is required to achieve the same level of runoff volume reduction in awetter location (or year) than in a drier location (or year). For example, in order to reducethe total runoff volume from a typical single family lot (on poor soils) to 10% or less of totalrainfall volume (i.e. the target condition):

� in a location where the annual rainfall is around 700 mm, about 3% of the lot would haveto be provided for infiltration

� in a location where the annual rainfall is around 1800 mm, about 15% of the lot wouldhave to be provided for infiltration

Variability in soil type and land use also has a big effect on the amount of area required tomeet a given volume reduction target (e.g. the 10% target), as discussed on the followingpages.

Effect of Rainfall on Infiltration Facility Performancesingle family lot (50% lot coverage)

poor soils (2.5 mm/h)

0

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% of Lot Used for Infiltration

Volu

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m L

ot(%

of t

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rain

fall)

BurnabyMountain(2675 mm)

NorthVancouver(2355 mm)

Maple Ridge(1811 mm)

North Surrey(1733 mm)

White Rock(1084 mm)

White Rock(2000 rainfall,709 mm)

Location and Anuual Rainfall (wet year 1999)

Infiltration Facility Type :

Bioretention facility with 150 mm of surface ponding on top of 1000 mm of absorbent soil

Figure 7-11


MAY 2002

7-19

Selecting Infiltration Facility DepthFigure 7-12 illustrates how the depth of an infiltration facility (i.e. distance from the bottomof the facility to the overflow level) increases the level of runoff volume reduction that canbe achieved for different types of facilities.

The benefits of increasing facility depth diminish beyond a certain threshold (around 500mm). Beyond this threshold, the area of an infiltration facility has a much greater impact onperformance than its depth (as discussed on the following pages).

It is important to note that shallow infiltration facilities typically provide the best opportunityfor recharging the soil interflow zone. In addition, the hydraulic conductivity of soils tendsto be higher closer to the surface.

Constraints on Facility DepthAppropriate depths for infiltration facilities must be selected based on site-specificcharacteristics and constraints.

As noted previously, the bottom of an infiltration facility should be at least 0.5 m above thelocal groundwater table. The depth to bedrock or to relatively impermeable soil layers mayalso govern the feasible depth of infiltration facilities.

Appropriate ponding depths for surface infiltration facilities may also be governed by safetyor aesthetic considerations.

Comparing Different Types of Infiltration FacilitiesFigure 7-12 shows that a soakaway pit would be slightly more effective than a bioretentionfacility of the same depth (with no surface ponding), because gravel stores more runoff perunit volume than absorbent soil (i.e. it has higher void space storage).

Placing an infiltration chamber in a soakaway trench (as shown in Figure 7-7b) increases itsstorage volume, and slightly improves its effectiveness. Similarly, surface ponding increasesthe storage capacity and improves the effectiveness of bioretention facilities, particularly forfacilities with fairly low absorbent soil depth (e.g. less than about 500 mm).

Effect of Depth and Facility Type on Infiltration Performance

010

2030

405060

7080

90100

0 500 1000 1500 2000

Depth of Absorbent Soil/Drain Gravel (mm)

Volu

me

of R

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f fro

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ot

(% o

f tot

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infa

ll)

Bioretention Facility(no surface ponding)

Bioretention Facility(with 150 mm ofponding on surface)

Soakaway (draingravel only)

Soakaway (withinfiltration chamber)

No Source Control

Type of Infiltration Facility� Multi-family lot (65% impervious coverage)� Infiltration Facility Area = 10% of Lot Area� Poor Soils (hydraulic conductivity of 2.5 mm/h)� North Surrey Rainfall (wet year, 1733 mm of rainfall)

Figure 7-12


MAY 2002

7-20

The Importance of Infiltration Area and Soil TypeFigures 7-13a and 7-13b show how the level of reduction in runoff volume and rate that canbe achieved using infiltration facilities is highly dependent on the hydraulic conductivity oflocal soils and on the amount of area provided for infiltration.

For example, providing 10% of a single family lot area for infiltration could:� reduce total runoff to about 10% of total rainfall and reduce the peak runoff rate from a

5-year storm by about 45%, where soils have good hydraulic conductivity (greater thanabout 13 mm/h)

� reduce total runoff to about 35% of total rainfall but achieve virtually no reduction in thepeak runoff rate from a 5-year storm, where soils have very poor hydraulic conductivity(about 1 mm/h)

Note that these graphs are based on Water Balance Model simulations for a very wet year inNorth Surrey (1999). In locations and/or years with less rainfall, infiltration facilities can beexpected to perform better than the graphs indicate (and vice versa).

These graphs assume that all undeveloped areas have disturbed surface soil (i.e. no absorbentlandscaping), and that runoff from disturbed soils on building lots is not captured bybioretention facilities.

Determining What is Feasible and AffordableThe size of infiltration facility that can be provided in any given situation will depend on:� the physical constraints associated with the available undeveloped space (feasibility

thresholds), and/or� willingness to pay (affordability thresholds)

Affordability thresholds will likely govern infiltration facility sizes for lower coverage landuses (e.g. single family residential) and feasibility threshold will likely govern for highercoverage land uses (e.g. commercial land uses).

The affordability thresholds shown on the adjacent infiltration performance curves are forillustration purposes only, and reflect judgement as to what seems appropriate. Furtherdiscussion on how to establish affordability and feasibility thresholds is provided on thefollowing page.

Infiltration Facility Performance (Runoff Rate Reduction) 50% lot coverage (e.g. single family)

0

5

10

15

20

25

0 5 10 15 20 25

% of Lot Used for InfiltrationPe

ak R

unof

f Rat

e fro

m

5-yr

Sto

rm

(L/s

per

hec

tare

) Very Low (1mm/h)

Low (2.5mm/h)

Medium toHigh (greaterthan 13 mm/h)

No SourceControl

Hydraulic Conductivity of

Local Soils

Feasibility Threshold

Affordability Threshold

Infiltration Facility Performance (Runoff Volume Reduction) 50% lot coverage (e.g. single family)

0102030405060708090

100

0 5 10 15 20 25


Volu

me

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al ra

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Very Low (1mm/h)

Low (2.5mm/h)

Medium (13mm/h)

High (50mm/h)

No SourceControl




Local Soils

Infiltration Facility Typebioretention facility with 150 mm of pondingdepth on top of 1000 mm of absorbent soil

Figure 7-13b

Figure 7-13a

Infiltration Facility Typebioretention facility with 150 mm ofponding depth on top of 1000 mm ofabsorbent soil

North Surrey Rainfall (wet year, 1733 mm annual rainfall)

North Surrey Rainfall (wet year, largest event: 5-year winter storm)

* refers to the rate of runoff from an entire development area (i.e. building lots and the roads serving these lots).

*


MAY 2002

7-21

Feasibility ThresholdsAs lot coverage increases there is less space available to locate infiltration facilities. Thefeasibility threshold refers to the maximum amount of physical space that could be used forinfiltration.

These thresholds will be highly site-specific because they depend on the layout ofimpervious and pervious spaces within a lot (or road), as well as on soil type.

It is typically not possible to use all undeveloped lot space for infiltration facilities.Feasibility thresholds can be estimated at about 50% of undeveloped lot space to provide astarting point for planning purposes.

Since constant wetting can cause localized expansion of clay soils, a certain amount ofclearance between infiltration facilities and building foundations (and property boundaries) isneeded to prevent potential damage. A clearance distance of 3 m or more should be used inany soils with significant clay content. For heavy clay soils, the clearance distance should beabout 5 m.

With proper engineering, it may be feasible to use nearly all of the undeveloped space withinroad right-of-ways for infiltration.

Affordability ThresholdsIncreasing the size of infiltration facilities improves their effectiveness (as shown in Figures7-13a and 7-13b), but also increases their cost. Local governments must establishaffordability thresholds based on the community’s willingness to pay, and on the potentialbenefits of the infiltration facilities.

Note that reductions in runoff volume and rate are indicators of hydrologic benefits, whichtranslate into benefits for a community in the form of stream protection and restoration,avoided flooding, or other avoided drainage costs.

Establishing Affordability ThresholdsFigure 7-14 shows an example of how order-of-magnitude cost estimates can provide astarting point for answering the questions:

� what can realistically be achieved through infiltration?� are infiltration source controls worth pursuing?� what is the likely return on investment?

The costs of infiltration facilities can be highly variable depending on site-specificconditions, such as amount and type of material that needs to excavated. The benefits ofinfiltration facilities are also highly dependent on site-specific conditions, and therefore, site-specific cost-benefit analyses are essential. The costs and benefits of infiltration facilitiesmust be considered in the context of an Integrated Stormwater Management Plan (ISMP).

Affordability Thresholds for Infiltration Facilities375 m2 urban single family lot (50% lot coverage)

0

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Low ($33per m2)

Average($100 perm2)

High ($166per m2)



Order-of-Magnitude Cost

Estimates*

* Source: U.S. EPA, 2000Low Impact Development: A Literature Review

Example: For $3000 per lot, from5% to 25% of an urban singlefamily lot area could be used forinfiltration, depending on sitespecific conditions

Figure 7-14


MAY 2002

7-22

Infiltration Facilities for Land Uses with High Impervious CoverageFigures 7-15a and 7-15b show the level of runoff volume and rate reduction that could beachieved for land uses with relatively high impervious coverage, such as high-densitymultiple family or commercial land uses.

In this case, the feasibility threshold rather than the affordability threshold governs theamount of infiltration area that can be provided.

By providing the feasible amount of infiltration area (about 7.5% of the lot area), the volumeof runoff volume from a high coverage lot could be reduced to:� about 10% of total rainfall, where soils have good hydraulic conductivity (greater than

about 13 mm/h)� about 60% of total rainfall, where soils have very poor hydraulic conductivity (about 1

mm/h)

The peak runoff rate from a 5-year, long duration winter storm could not be reduced usinginfiltration facilities on high coverage land uses, even where soils have good hydraulicconductivity. This conclusion does not necessarily apply to lower rainfall locations.

The effectiveness of infiltration facilities on land uses with high impervious coverage can beimproved by providing additional storage structures such as cisterns, and releasing storedrunoff to infiltration areas at a controlled rate.

Performance of Infiltration Facilities for a Range of Land Use TypesThe GVRD report on the Effectiveness of Stormwater Source Control includes infiltrationperformance curves (similar to Figures 7-13 a-b and 7-15 a-b) for eight different land usetypes, with total lot coverage ranging from 30% (e.g. low-density single family) to 98% (e.g.town centre commercial).

The GVRD report also provides infiltration performance curves for four road types, withpaved roadway widths ranging from 8.5 m (e.g. local roads) to 16 m (e.g. divided arterials).Sample infiltration performance curves for roads are shown on the following page.

For a given land use or road type and soil condition, these curves can be used to estimate thehydrologic benefits (i.e. runoff volume and rate reduction) of providing a certain amount ofinfiltration area.

Infiltration Facility Performance (Runoff Volume Reduction) 85% lot coverage (e.g. high density multi-family)

0102030405060708090

100

0 5 10 15 20 25


Volu

me

of R

unof

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(% o

f tot

al ra

infa

ll) Very Low (1mm/h)

Low (2.5mm/h)

Medium (13mm/h)

High (50 mm/h)

No SourceControl


Local Soils

AffordabilityThreshold

FeasibilityThreshold

Infiltration Facility Performance (Runoff Rate Reduction) 85% lot coverage (e.g. high density multi-family)

0

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ate

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)

Very Low (1mm/h)

Low (2.5 mm/h)

Medium to High(greater than 13mm/h)

No SourceControl


Local Soils

AffordabilityThreshold

FeasibilityThreshold

Infiltration Facility Typebioretention facility with 150 mm ofponding depth on top of 1000 mmof absorbent soil

North Surrey Rainfall(wet year, 1733 mm annual rainfall)


North Surrey Rainfall(wet year, largest event:

5-year winter storm)

Figure 7-15b

Figure 7-15a


MAY 2002

7-23

Performance of Infiltration Facilities on RoadsFigures 7-16a and 7-16b show the reduction in runoff volume and rate that could be achievedusing infiltration facilities on roads. These graphs show the simulated performance of two-layer swale and infiltration trench systems, assuming:� top layer (surface swale) = 300 mm of absorbent soil� bottom layer (infiltration trench) = gravel-filled trench with perforated overflow pipe 300

mm above the trench bottom

The performance curves show that the runoff from a typical local road could be virtuallyeliminated (even during a very wet year) by dispersing roadway runoff to:

� a 2 m wide swale/trench (or two 1 m swales) along the road, where soils have very goodhydraulic conductivity (around 50 mm/h)

� a 4 m wide swale/trench (or two 2 m swales) along the road, where soils have goodhydraulic conductivity (around 13 mm/h)

Even where soils have very poor hydraulic conductivity (around 1 mm/h), a 4 m swale/trenchcould reduce the volume of runoff from a typical local road to about 25% of total rainfall.

In general, infiltration facilities along roads are more effective than on-lot infiltrationfacilities because there is typically less concentration of runoff (i.e. the ratio of imperviousarea to infiltration area tends to be lower).

Note that the affordability thresholds shown on Figure 7-16a and 7-16b are provided forillustration purposes only. Local governments should establish their own thresholds byevaluating costs, benefits and willingness to pay.

Infiltration Facility Performance (Runoff Rate Reduction) 8.5 m Paved Roadway (e.g. local roads)

0

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20

25

0 1 2 3 4 5 6

Width of Infiltration Swale/Trench (m)Pe

ak R

unof

f Rat

e fro

m 5

-yr S

torm

(L

/s p

er h

ecta

re) Very Low (1

mm/h)

Low (2.5mm/hr)

Medium (13mm/h)

High (50mm/h)

No SourceControl




Local Soils

* refers to the rate of runoff from an entire development area (i.e. building lots and the roads serving these lots).

Infiltration Facility Performance (Runoff Volume Reduction)8.5 m Paved Roadway (e.g. local roads)

010

20304050

607080

90100

0 1 2 3 4 5 6

Width of Infiltration Swale/Trench (m)

Volu

me

of R

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Roa

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ight

-of W

ay

(% o

f tot

al ra

infa

ll) Very Low (1mm/h)

Low (2.5mm/h)

Medium (13mm/h)

High (50mm/h)

No SourceControl




Local Soils

Represents the rateof runoff fromunmitigated buildinglots served bynetwork of roads

North Surrey Rainfall(wet year, 1733 mm annual rainfall)

North Surrey Rainfall (wet year, largest event: 5-year winter storm)

*

Figure 7-16a

Figure 7-16b


MAY 2002

7-24

Achievable Level of Runoff Volume Reduction for Different Land Use TypesFigure 7-17 provides an estimate of the level of runoff volume reduction that could beachieved using infiltration facilities (during a wet year in the South Coast climate) for arange of land use types, under different soil conditions. This figure assumes that infiltrationfacility size is based on the governing threshold for each land use type (i.e. either feasibilityor affordability).

Where soils have medium or better hydraulic conductivity (greater than about 13 mm/h),runoff volume could be reduced to about 10% of total rainfall (i.e. the target condition for ahealthy watershed) for all but the highest coverage land uses (high density multiple family orcommercial).

To achieve the 10% target for lower coverage single family land uses, absorbent landscapingwould be required in addition to infiltration facilities. This is because lots with lowerimpervious coverage typically have more runoff volume from disturbed soil (Figure 7-13assumes that undeveloped areas are covered by disturbed soil).

Significant levels of runoff volume reduction can also be achieved in soils with poorconductivity (around 2.5 mm/h), for all but the highest coverage land uses. Even where thehydraulic conductivity of soils is very poor (around 1 mm/h), runoff volume can be reducedby about 40 to 50% on single family and low to medium-density multiple family land uses.

Note that greater levels of runoff volume reduction would likely be achievable in locationsand/or years with less rainfall (and vice versa).

Typical hydraulic conductivity ranges for different soil types are provided below forreference purposes.

Soil Type Typical HydraulicConductivity Range*

� Sands and gravels > 50 mm/h� Sandy loams 10 – 50 mm/h� Silty loams 5 – 40 mm/h� Clay loams 2 – 6 mm/h� Clays < 2 mm/h

Achievable Level of Runoff Volume Reduction Using Infiltration Facilities


0

10

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20 30 40 50 60 70 80 90 100Percent Impervious Lot Coverage

Volu

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(% o

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ll)

Very Low (1mm/h)

Low (2.5 mm/h)

Medium to High(greater than 13mm/h)

No Source Control

single familymultiple family commercial

Hydraulic Conductivity of Local Soils

Figure 7-17



* Source: Soil Texture Triangle: Hydraulic Properties Calculator, Washington State University(http://www.bsyse.wsu.edu/saxton/soilwater/)


MAY 2002

7-25

Creating Hard Surfaces that InfiltratePervious PavingRunoff from paved surfaces can be virtually eliminated by replacing impervious pavementwith pervious pavers that allow rainwater infiltrate through cracks between the pavers.Figure 7-18 shows an example of pervious paving.

Pervious pavers are placed over a reservoir base course of fractured drain rock (similar torailway ballast), which can be sized to store a given design storm. For example, to store a60mm storm, the reservoir part of the base course would have to be about 180 mm deep(33% void space).

Pervious paving can be applied on areas with light (or no) vehicle traffic (e.g. driveways,shoulders of roadways, sidewalks, overflow parking areas).

Figure 7-19 provides an example of how pervious paving options for roadways can reducerunoff volume.

Since pervious paving effectively reduces the impervious coverage on lots or road right-of-ways, applying pervious paving can also improve the effectiveness of infiltration facilities(by reducing the concentration of runoff discharged into these facilities).

Volume Reduction Benefits of Pervious Paving Typical Collector or Large Local Road

11 m Paved Roadway (6 m travel way + two 2.5 m parking lanes) Two 1.5 m sidewalks

0102030405060708090

100

no pervious paving pervious sidewalks pervious sidewalks &parking lanes

Pervious Paving Options for Road

Volu

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ight

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(%

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� North Surrey Rainfall (wet year, 1733 mm annual rainfall)

� 300 mm of drain rock beneath pervious pavers

Figure 7-19

Figure 7-18 Pervious Pavers


MAY 2002

7-26

Pervious DecksRunoff from decks or patios can be virtually eliminated by using wood decks with spacebetween the boards (see Figure 7-20) rather than impervious surfaces such as concrete.

Rainfall hitting a spaced wood deck flows to the ground below, and provided there is areasonable depth of absorbent soil beneath the deck, runoff from the deck is eliminated.

This is an example of a simple, well-known, site design strategy that can effectively reduceimpervious coverage and promote infiltration.

Figure 7-20 Pervious Decks


MAY 2002

7-27

Applying Combinations of Infiltration StrategiesFigure 7-21 illustrates an example of the installation of selected infiltration techniques on atypical single-family lot, where the performance target is to capture and infiltrate 60 mm ofrainfall per day in order to provide both rainfall capture and runoff control in an on-parcelsystem.

� Roof drain leaders outfall through a debris catcher to an array of infiltration chambers(see Figures 7-7a and 7-7b) in the front lawn. In order to infiltrate the runoff from the280 m2 roof, a 7.6 m x 6 m infiltration areas is provided. This could be entirely in thefront yard, or could be split over various locations in the yard based on soilcharacteristics and landscaping objectives.

� The infiltrator chambers have an overflow pipe connected to the street storm drainsystem that allows rainfall events that exceed the storage capacity to overflow.

� The plan also shows an interceptor perforated drain along the downstream propertyboundary. This is shown as an illustration only. It could be installed as required on lotswith steep slopes or seepage problems to remove surface water and shallow interflowand deliver it to the storm drain system. Ideally, there should be at least 9 m between theinfiltration chamber and the perforated drain. This would provide an approximately 30-day delay between the time that water is absorbed as interflow and the time it is removedby the perforated drain. The 30-day delay is based on a moderate 12.5 mm/h infiltrationand interflow rate. Delays between infiltration chamber and footing drains would followa similar pattern, where each foot of interflow distance represents a day or more of delay.

� The bulk of the site is maintained with absorbent soils. Special care is taken to ensurethat the top 300 mm of soil are highly absorbent, by avoiding compaction and ensuringhigh organic matter content.

� Driveway and surface paving is shown as permeable pavers, with a reservoir base course.This ensures that rainfall landing on the driveway is stored underground and allowed tosoak into the underlying soils.

� The rear outdoor living area is a spaced wood deck over absorbent ground. This allowsrainfall to bypass the deck and infiltrate into the ground below. See Figure 7-20 fordetails.

� Reducing the building roof area on the site would reduce the amount of infiltrationchamber area required.

Figure 7-21


MAY 2002

7-28

Infiltration Strategies for Land Uses with High Levels of Surface ParkingFigure 7-22 shows an example of infiltration strategies for a typical commercial land usewith extensive surface parking areas. This Figure shows how a combination of swales withinfiltration trenches and bioretention areas could be integrated into parking lot design toinfiltrate runoff from rooftops and paved surfaces.

Figure 7-22 Designing Parking Lots that Infiltrate


MAY 2002

7-29

Cost Implications of Infiltration FacilitiesThe costs of infiltration facilities are highly variable and depend on site-specific conditionssuch as soil type, topography, the scale of installation, and infiltration facility design.Typical installation costs for infiltration facilities range from about $30 - $170 per m2 .

The operation and maintenance requirements for surface facilities are mainly aesthetic (e.g.landscape maintenance). Annual operation and maintenance costs for surface infiltrationfacilities are typically in the range of 5-10% of capital costs.

Operation and maintenance requirements for sub-surface facilities are less frequent but canbe more costly (e.g. periodic cleaning of soakaway trenches). Annual operation andmaintenance costs for sub-surface infiltration facilities are typically in the range of 5-20% ofcapital costs.

Pervious Paving CostsThe cost of installing of pervious paving is typically in the range of $20 - $30 per m2,depending on the design and site conditions. This is significantly more expensive thanconventional paving (approximately $5 - $10 per m2). Also, the operation and maintenancecosts associated with vacuum sweeping may be substantial if a community does not alreadyhave the necessary equipment.

Design and Construction Tips for Infiltration Facilities� Site-specific percolation tests should be carried out (ideally under saturated soil

conditions) to determine the hydraulic conductivity of soils on a development site,and to identify suitable infiltration areas. Percolation tests should be performed atthe depth of proposed infiltration facilities.

� Infiltration facility sites should be protected during construction from compactionand sedimentation, by pre-identifying and fencing, or other means. Inadvertentcompaction should be removed by ripping or scarifying the site prior to installationof infiltration facilities.

� Infiltration facilities should be placed over undisturbed or lightly compacted ground(about 80% modified proctor density) to maximize exfiltration of rainfall into theunderlying subsoil.

� Adequate sediment and erosion control during construction is essential to preventclogging of infiltration facilities and underlying soils.

� Pipes leading to infiltration facilities should be fitted with debris catchers andcleanouts to minimize the movement of sediment and debris into the facilities. Thisis particularly important for sub-surface infiltration facilities.

� Infiltration facilities should be designed with pathways to allow overflow to escapeto downstream watercourses via a storm drain system or overland flow.

Tips for Bioretention Facilities� Low points of bioretention facilities should be planted with flood-tolerant plants.

� Higher areas should be planted with streamside or upland species. Examples ofappropriate bioretention plants are shown below:

Frequency of Flooding Botanical Name Common Name

Winter standing water Juncus spp. RushOccasional standing water Carex spp. SedgeRare flooding Spiraea douglasii HardhackNo flooding Rosa spp. Shrub rose

These plants would work best in coastal climates, but may also be used in other partsof the province. Appropriate plant species will vary across the province dependingon biogeoclimatic zone.

� Soils in bioretention areas should have the characteristics of absorbent soils,discussed in Section 7-3.

� Bioretention facilities should be constructed in the dry season whenever possible, orthey should be totally isolated from flows during construction, to protect other partsof the drainage catchment form sedimentation.

� In areas where soils are relatively impermeable, bioretention facilities can bedesigned with a sub-drain to slowly remove water that infiltrates through theabsorbent soil layer. This filters out sediments and many pollutants.


MAY 2002

7-30

Tips for Pervious Pavers� Pervious paving systems are at risk of being plugged by silt or organic debris that

washes onto the surface layer. To avoid this risk, careful attention should be paid toprotecting the pervious paving from sedimentation during construction. In addition,most pervious pavement systems are designed with a high factor of safety forpermeability e.g. often the permeability at time of construction is 10 times thatrequired for the successful performance of the pavement (i.e. a Factor Of Safety of10).

� The pervious paving system includes a special base course under the pavingdesigned to hold the stormwater until it has time to soak into the ground below. This‘reservoir’ base course is often made of fractured drain rock (railway ballast) that hasabout 33% void. The depth of the base course is designed with the storage capacityfor stormwater as one consideration, with the surface live load and bearing capacityof the underlying soils as other factors. Generally, the deeper the base course, themore stormwater holding capacity and the greater the structural strength. Slope onthe pervious pavers should be between 1% and 6%. Calculation of the reservoircapacity should consider any drainage areas flowing to the pavement.

� Pervious paving should not be used on any stormwater quality ‘hot spot’ wheresurface contaminants may be concentrated and enter the groundwater (e.g. gasstations, wrecking yard, fleet storage yards, or other sites that store hazardousmaterials).

� A vertical pipe inlet should be installed so that the reservoir base course overflows toa storm drain when full.

Operation and Maintenance Tips for Infiltration Facilities� Sediment and debris must be regularly removed from debris catchers and cleanouts.

� Periodic cleaning of infiltration facilities will likely be required to removeaccumulated sediment and maintain hydraulic performance.

Tips for Bioretention Facilities� Provisions for dry season watering of plants in bioretention facilities is essential,

especially in the plant establishment period.

� Normal landscape maintenance, with an emphasis on minimum inputs of fertilizerand integrated pest management is appropriate.

Tips for Pervious Pavers� Where pervious paving is used, regular street sweeping with vacuum and brush

machinery is needed to remove surface sediment and organics that may enter thecracks and reduce permeability.

� Low traffic areas (e.g. roadway medians) may experience some weed growth in thecracks (which is a problem for any paved surface). Steam-based weeding systemsare available to efficiently manage weed growth without use of herbicides.

� Snow clearing of properly installed pervious pavements can be achieved withstandard equipment. Following the manufacturer’s design specifications shouldeliminate any significant freeze-thaw issues.


MAY 2002

7-31

7.6 Type 3 Source Control - Green RoofsReplacing impervious rooftops with green roofs can significantly reduce the volume and rateof runoff from building lots. A layer of absorbent soil and vegetation on top of building andparkade rooftops can retain rainfall and allow it to evaporate or transpire. The runoff from agreen roof passes through the absorbent soil layer to an underdrain layer (there is no surfacerunoff), and thereby attenuates peak runoff rates.

Green roofs are classed into two categories: extensive green roofs which typically have ashallow soil profile of 20 to 100 mm and support mosses, grasses and sedums; and intensivegreen roofs with soil depths greater than 100 mm able to support substantial vegetation(shrubs, trees, etc.). Intensive green roofs are typically landscaped features that require moremaintenance than extensive green roofs.

Green roofs are common in many parts of Europe and are becoming more common in NorthAmerica. They are often applied for reasons other than stormwater management; engineeredgreen roofs may also provide heating or cooling savings by insulating buildings, as well asaesthetic benefits, air quality benefits, and reductions in the ‘urban heat island’ effect.

Figure 7-23 shows a lightweight extensive green roof on an airport building. Figure 7-24shows an example cross-section of an intensive green roof over a parking garage.

Figure 7-24

Figure 7-23 Lightweight Extensive Green Roof


MAY 2002

7-32

The Effectiveness of Green Roofs under Different Rainfall ConditionsFigure 7-25 shows that green roofs provide more significant reduction in runoff volumewhere (and when) total annual rainfall is lower. As total rainfall decreases, a greaterpercentage of total rainfall becomes evapotranspiration.

Green roofs would be most effective at reducing runoff volumes in drier parts of theprovince, and would be more effective in drier years as opposed to wet years.

In terms of reducing runoff volume, extensive green roofs can be almost as effective asintensive green roofs.

Effect of Rainfall on Green Roof Performance Medium Density Multi-Family Lot (70% lot coverage, mostly rooftop)

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With ExtensiveGreen Roofs (soildepth shown)

North Surrey(wet year, 1999)White Rock

(dry year, 2000)

Burnaby Mountain (wet year, 1999)500 mm

50 mm

100 mm300 mm

Figure 7-25


MAY 2002

7-33

The Importance of Green Roof Soil DepthIncreasing the depth of absorbent soil increases the retention capacity of green roofs. Thisdecreases the volume and rate of green roof runoff, as shown in Figures 7-26a and 7-26b.

The volume reduction benefits of increasing green roof soil depth diminish beyond about 70mm.

In order to maximize the reduction in runoff rates from large, prolonged storms that occurduring wet weather periods, intensive green roofs with about 300 mm of soil depth areneeded (see Figure 7-26a). Where building structural limitations do not permit this soildepth, green roofs with shallower soil profiles may still be able to achieve significantreductions in runoff rates from long duration wet weather storms that are less extreme and/orin locations with less rainfall.

Significant reduction in runoff rates from short intense storms (i.e. cloudbursts) that occurduring dry weather periods can be achieved using extensive green roofs with 100 m of soildepth (see Figure 7-26b).

Figure 7-26b shows the runoff rate from an extremely intense cloudburst (100-year returnperiod) that occurred in White Rock on June 8th, 1999. This event is discussed in more detailin Section 7.8.

Effect of Soil Depth on Green Roof PerformanceMedium Density Multi-Family Lot (70% lot coverage, mostly rooftop)


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Intensive Green Roofs

Extensive Green Roofs

Total Annual rainfall = 1733 mm

Peak Event Description: - 77 mm of rainfall over 20 hours - Maximum intensity = 9 mm/hr - Total rainfall in 5 preceding days = 50 mm

Representsimperviousrooftopcondition

Effect of Soil Depth on Green Roof PerformanceMedium Density Multi-Family Lot (70% lot coverage, mostly rooftop)

White Rock Rainfall (wet year, 1999)

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Extensive Green Roofs

Total Annual rainfall = 1083 mm

Peak Event Description: - 63 mm of rainfall over 7 hours - Maximum intensity = 30 mm/hr - Total rainfall in 5 preceding days = 10 mm

Representsimperviousrooftopcondition

Figure 7-26a

Figure 7-26b


MAY 2002

7-34

Benefits of Green Roofs for Different Land UsesFigures 7-27a and 7-27b show that the benefits of green roofs, in terms of reducing runoffvolume and rate, is most significant for land uses with high percentages of rooftop coverage,such as high density multi-family or commercial uses (without substantial surface parking).Green roofs have less benefit for single family land uses, and it is likely less feasible toimplement green roofs on single family buildings.

The Importance of Parking TypeNote that the type of parking provided for multi-family and commercial land uses has a bigimpact on the potential benefits of green roofs (green roofs can be applied to parkades butnot to surface parking). Figures 7-27a and b show modeling results for multi-family andcommercial land uses with limited surface parking (i.e. rooftop coverage is approximatelyequal to impervious coverage).

Benefits of Green Roofs for Different Land Uses(Runoff Rate Reduction)


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Benefits of Green Roofs for Different Land Uses(Runoff Volume Reduction)


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Figure 7-27b

Figure 7-27a


MAY 2002

7-35

Cost Implications for Green RoofsThe costs of green roofs are highly variable and depend on site-specific conditions, such asthe scale of installation, vegetation type and green roof design. Typical installation costs forgreen roofs infiltration facilities range from about $60 to $150 per m2 (intensive green roofswith 300 mm or more of soil depth are likely to be near the high end of this range). Theremay also be increased structural costs (although this is not likely a factor for concretebuildings).

Note that the scale of the installation alone can influence the installation cost of green roofsby a factor of 3 or more. This is a direct consequence of the fact that the present market forgreen roofs in North America is too small to be economically efficient. The cost of installinggreen roofs in Germany (where a mature green roof industry exists) is typically half the costof a similar installation in North America.

Annual operation and maintenance costs for green roofs are typically in the range of $1 to$2.50 per m2. Operation and maintenance costs are typically highest in the first year whenplants may require establishment watering, weeding, and some replacement.

Design and Construction Tips for Green Roofs� To reduce structural costs, the design of the absorbent soils over the parking garage

lid or roof may use a light weight growing medium. The depth of the soil related toits absorbency may also be fine-tuned for structural load efficiency.

� If light-weight soils are used, they can be subject to wind erosion when they dry out.Appropriate scheduling of soil placement, and temporary protection of the soils untilplanted or watered should be arranged.

� Roof water should be kept separate from runoff from paved surfaces, which can bepolluted with hydrocarbons and heavy metals. Whereas paved surface runoff mayrequire treatment, most green roof runoff will be clean enough to be released directlyto storage and receiving waters.

� Proper waterproofing and flashing are essential for green roofs.

� Most green roof systems include a root growth inhibitor to keep roots from invadingthe waterproof membrane area.

� The most successful green roof systems use drought tolerant plants, and avoidgrasses.

� Establishment watering may be required, using either surface standard wateringdevices, or an automatic irrigation system. Watering requirements will vary basedon the green roof system chosen.

Operation and Maintenance Tips for Green Roofs� Intensive roofs are typically landscaped features that require a higher level of

maintenance than extensive green roofs. Through proper plant selection, it may bepossible to design extensive green roofs that are essentially self-sustaining andrequire very little maintenance.

� Irrigation, fertilization and pesticide/herbicide application should be kept to aminimum. Occasional weeding of wind-blown seeded plants may be required.

� Storage in a plastic drainage layer, or equivalent storage volume in drain rock, underthe green roof soil can increase the effective rainfall capture and storage volume.

� The drainage outflow from the parking garage lid should be connected to infiltrationfacilities, in suitable areas of the site off the parking garage, with an overflow to thestorm drain system.

� Drain inlets from green roofs will require regular inspection (as is normal practice).

� Normal landscape maintenance techniques should suffice for the absorbent soils ongreen roofs. Landscaping contractors must be made aware of the need to avoiddamaging roof membranes during maintenance activities.


MAY 2002

7-36

7.7 Type 4 Source Control - Rainwater Re-useJust as the trees in a forest use a significant portion of rainfall, capturing rainfall for humanre-use can play a key role in managing the Water Balance at the site level. The benefits ofrainwater re-use go beyond stormwater management (i.e. reducing the volume and rate ofrunoff from developed areas). Re-use can also reduce the amount of water drawn fromreservoirs and reduce the costs of water supply infrastructure.

In general, the most significant reductions in runoff volume can be achieved by capturingand re-using rainwater for indoor greywater type uses, particularly for land uses with highrates of water use. Re-using rainwater for irrigation typically provides less benefit in termsrunoff reduction because the demand for irrigation water occurs during the dry weatherperiods, and most runoff occurs during wet weather periods.

For rainwater re-use on single family residential land uses, rooftop runoff is typically storedin rain barrels (see Figure 7-28a). For re-use on multiple family, commercial or institutionalland uses, rooftop runoff is typically stored in cisterns or detention vaults (e.g. see Figure 7-28b).

Rainwater re-use systems can be combined with infiltration facilities as shown schematicallyin Figure 7-28b. In catchments where maintaining stream base flows is a key objective, firstpriority may be given to groundwater recharge, with only surplus water applied to in-building re-use.

Figure 7-28a Rainwater Re-use using Rain Barrels

Figure 7-28b Rainwater Re-use using Cisterns


MAY 2002

7-37

Benefits of Rainwater Re-use for Different Land UsesSignificant reductions in runoff volume can be achieved on high-density residential land usesby capturing and re-using rooftop runoff for toilets and washing machines, as shown inFigure 7-29a. As population density increases, residential water use rates increase, andtherefore, the level of reduction in runoff volume that can be achieved through rainwater re-use increases.

The level of volume reduction that can be achieved by re-using rainwater for greywater uses(toilets and washing machines) on commercial land uses varies significantly depending onthe type of commercial land use, as shown in Figure 7-29b. Commercial land use types withhigh water use rates, such as restaurants and bars, can achieve significant runoff reduction,even where density is low (e.g. local commercial).

Note that rainwater re-use for greywater uses is most beneficial on high-coverage land useswhere opportunities for infiltration are most limited.

Benefits of Rainwater Reuse for Commercial Land Uses(Runoff Volume Reduction)


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Benefits of Rainwater Reuse for Residential Land Uses(Runoff Volume Reduction)


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Storage volume provided =300 m3 per hectare of rooftop


Figure 7-29b

Figure 7-29a




MAY 2002

7-38

The Impact of Surface ParkingThe potential benefits of rainwater re-use are significantly less for land uses that havesignificant amounts of surface parking, as shown in Figures 7-30. This reflects theassumption that runoff from paved surfaces is less suitable for indoor re-use, primarily due towater quality concerns (although it may be possible with appropriate treatment).

The Effectiveness of Rainwater Re-use under Different Rainfall ConditionsGreater reductions in runoff volume can be achieved through rainwater re-use where (andwhen) total annual rainfall is lower, as shown in Figure 7-31. As total rainfall decreases,water use rates (a function of land use type) become a greater percentage of total rainfall.

In certain situations it may be possible to re-use virtually all rooftop runoff. However, it isimportant that rainwater re-use systems be designed to ensure that adequate baseflow ismaintained in downstream watercourses.

Effect of Rainfall on the Benefits of Rainwater Reuse Multi-family Lot (90 dwelling units per ha, 68% rooftop coverage)

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White Rock(dry year, 2000)

Burnaby Mountain (wet year, 1999)

Impact of Surface Parking on Effectiveness of Rainwater Reuse(Residential Land Uses) North Surrey Rainfall (wet year, 1999)

Rainwater Reuse for Toilets & Washing Machines

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Figure 7-30

Figure 7-31



MAY 2002

7-39

Selecting an Appropriate Storage VolumeIncreasing storage volume (i.e. size of rain barrels or cisterns) can improve the hydrologicbenefits of rainwater re-use, as shown in Figure 7-32. The volume reduction benefits ofproviding additional storage capacity diminish beyond a relatively low threshold (about 100m3 per hectare of rooftop). Beyond this threshold, runoff volume reduction is primarily afunction of land use characteristics (e.g. population density, commercial density, land usetype and type of parking).

Figure 7-32 also shows that very large storage volumes are needed to achieve any significantreduction in peak runoff rates from extreme rainfall events (e.g. a 5-year winter storm).

Note that this figure is based on Water Balance Model simulations for a very wet year in theGVRD (1733 mm annual rainfall). In locations and/or years with less rainfall, it is likely thatthe same benefits could be achieved using with less storage volume (and vice versa).

Effect of Storage Volume on Benefits of Rainwater ReuseMulti-family lot (150 dwelling units per ha, 67% rooftop coverage)

Rainwater reuse for toilets and washing machinesNorth Surrey rainfall (wet year, 1999)

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Volume of Runoff(from lot only)

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Figure 7-32


MAY 2002

7-40

Cost Implications of Rainwater Re-useThe design and costs of rainwater re-use systems must be considered in the context of site-specific characteristics, including:

� nature of the development (e.g. water use characteristics, design of individualbuildings)

� site-specific rainfall patterns

� characteristics of both stormwater and water supply infrastructure (existing orplanned)

Costs implications must be considered at the scale of individual building (e.g. cisterns,additional pipe), as well as at the larger site (or regional) scale (e.g. water use savings,reduction in size of water supply and/or stormwater infrastructure). It is not possible toprovide generalized costs estimates for rainwater re-use.

Design and Construction Tips for Rainwater Re-use

� Rainwater re-use systems may be designed to slowly release small amounts of waterin order to maintain stream baseflows.

� Rainwater re-use systems in major buildings would require mechanical engineeringdesign.

� There are traditional and evolving new systems for use in single family or smallbuildings. Some store rainwater right at the eaves, and more traditional systemsinclude rain barrels or plastic vaults with either gravity or pump feed.

� Refer to publications on the subject for details of cistern pre-treatment anddewatering systems. Access for vacuum hose cleaning from a truck is advisable.

� Storage cistern designs are subject to waterproofing and structural engineering.

Operation and Maintenance Tips for Rainwater Re-use

� To reduce contamination of water stored in cisterns, the source of water shouldgenerally only be roofs, or other clean sources.

� Occasional cleaning of cisterns may be necessary. This is usually performed byvacuum hose.

� Regular inspection of cisterns is required to ensure that control structures continue tofunction properly.


MAY 2002

7-41

7.8 Applying Source Controls to MitigateExtreme Cloudbursts

One of the anticipated effects of climate change is an increase in the frequency ofcloudbursts – high intensity short duration storms - which could cause significant drainageproblems.

An extremely intense cloudburst (100 year short duration storm) occurred in White Rock onJune 8th, 1999 and caused extensive flood damage. The simulated runoff hydrographs (froma typical multi-family neighbourhood) shown in Figure 7-33 demonstrate how effective thefollowing source control scenarios would be at reducing the runoff from this event:

� Scenario 1: No Source Control - All impervious area is directly connected to a stormsewer system and pervious areas are covered by disturbed soil.

� Scenario 2: Absorbent Landscaping - Disturbed soil is replaced with 300 mm ofabsorbent landscaping; peak runoff rate would be reduced by about 27%.

� Scenario 3: Absorbent Landscaping plus On-Lot Infiltration Facilities – Same asScenario 2 except that all lots have bioretention facilities (150 mm of surface ponding ontop of 1 m of absorbent soil) covering 10% of lot area; peak runoff rate would be reducedby about 70%.

� Scenario 4: Absorbent Landscaping plus Intensive Green Roofs - Same as Scenario 2except that all residential buildings and parkades have green roofs with 300 mm of soildepth; peak runoff rate would be reduced by about 80%. Note that the same level ofrunoff rate reduction could be achieved using green roofs with extensive green roofs thathave 100 mm of soil depth (see Section 7.6).

� Scenario 5: Absorbent Landscaping plus Intensive Green Roofs plus On-StreetInfiltration Facilities – Same as Scenario 4 except that all roads have one 3 m wideinfiltration swale/trench system (as described in Section 7.5) within road right-of-ways;peak runoff rate would be reduced by about 92%.

This case study shows that source controls can be very effective at reducing runoff rate fromcloudbursts, and thus partially mitigating some of the anticipated effects of climate change.

Another anticipated effect of climate change is an increase in the amount of fall/winterrainfall, which will increase total runoff volume. The watershed case studies presented inChapter 8 show that source controls can also be effective at mitigating this effect of climatechange.

Effectivess of Source Controls at Reducing Peak Runoff from an Intense Cloudburst

Multi-family neighbourhood (72% coverage on lots, no surface parking, 11 m wide roads)

Poor soils (hydraulic conductivity of 2.5 mm/hr)

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Scenario 4 - AbsorbentLandscaping + GreenRoofs

Scenario 5 - AbsorbentLandscaping + GreenRoofs + On-streetInfiltration

Figure 7-33

Total rainfall = 63 mm


MAY 2002

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7.9 Communicating Performance Targets to DevelopersTo achieve performance targets, appropriate stormwater management practices must beintegrated with site design. For this to happen, performance targets must be clearlycommunicated to developers in a format that they can apply to the design of stormwatersystems at the site level.

Case Study Example: Design Guidelines for DevelopersInfiltration has been identified as the most applicable source control option in the City ofChilliwack.

Chilliwack’s Design Guidelines for Stormwater Systems provide step-by-step procedures forland developers to follow in order to design infiltration and detention systems that meet theCity’s design criteria for rainfall capture and runoff control. This example shows how tocommunicate performance targets and design criteria to developers. These Guidelines alsospecify performance monitoring requirements.

The Design Guidelines consist of the following forms:

� Form 1 - Development Site Summary Characteristics

� Form 2 – Criteria for Absorbent Landscaping

� Form 3 – Design of Infiltration Facilities

� Form 4 – Design of Detention Facilities

� Form 5 – Performance Monitoring Requirements

These forms are reproduced on the following pages.


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Form 1 – Development Site Summary Characteristics

Total development site area:

� Atotal = _______ ha

Minimum hydraulic conductivity of on-site soils (from on-site percolation testing):

� H = _______ mm/hr

Total impervious area on development parcels (excludinggreen roofs):

� IAon-lot = _______ ha

Total impervious area on roads (excluding perviouspaving):

� IAroad = _______ ha

Total impervious area on development site

� IAtotal = IAon-lot + IAroad = _______ha

Total pervious area on development site

� PAtotal = Atotal – IAtotal = _______ha

Site and Key Plan

Form 2 - Criteria for Absorbent Landscaping

The design guidelines presented in Forms 3 and 4 are based on impervious areas only.

On-site pervious areas must be ‘self-mitigating’ (i.e. meet rainfall capture and runoff control targets).In order to achieve this:

� Minimum depth of absorbent soil* for on-site pervious area = 300 mm* must meet BC Landscape Standard for medium or better landscape. The range of acceptablesoil textures is shown below:

Lightest Soil:Sand 90%Silt/Clay 5%Organic Matter 5%

Typical Design Soil:Sand 75%Silt/Clay 15%Organic Matter 10%

Heaviest Soil:Sand 55%Silt/Clay 25%Organic Matter 20%

City of Chilliwack – Design Guidelines for Stormwater SystemsProcedure for Sizing Infiltration and Detention Facilities


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Form 3 – Design of Infiltration FacilitiesRainfall capture criteria: capture and infiltrate 300 m3 of rainfall per day per impervious hectare

Infiltration facilities are to be provided as follows:

� On individual development parcels to capture runoff from rooftops and parking areas (e.g. by means of on-lot soakaways)

� Within road right-of ways to capture runoff from paved roadway (e.g. by means of roadside infiltration trenches)

Sizing Infiltration Facilities(applies for both development parcels(1) and roads)Step 1) Select Design Depth, D D = _____ m

D = distance from bottom of infiltration facility to the maximum waterlevel (the point where overflow occurs)

Step 2) Select Facility Type and Determine Effective Depth, Deff

Deff = [D x VS] = _____mVS = void space storage, the ratio of the volume of water retained perunit volume of the infiltration facility. Typical values for different typesof infiltration facilities are shown in Table B on the following page.

Step 3) Determine Minimum Footprint Area, A (i.e. bottom area)needed to meet rainfall capture target

Amin = [ (____ m2, from Table A) x (_____ m2 of IA served)] / 1000

A = the total area (in plan view) covered by the infiltration facility

(1) A typical facility size may be developed for multiple lots that have similar soilcharacteristics and similar amounts of IA.

Conveyance ofOverflow fromInfiltration Facilities

Overflow from infiltrationfacilities (on-lot and on-road) should be conveyedinto runoff control facilities(refer to Form 3) via astormwater drainagesystem, most likely withinthe road ROW. Roaddrainage may consist of:

a) a perforated pipe atthe top of an infiltrationtrench

b) a catch basinconnected to stormsewer pipe

c) a surface swale

Providing Runoff Control Storage in Infiltration Facilities (Optional)Increasing the dimensions of infiltration facilities (whether they are on on-lot or on-road above theminimum requirement (i.e. A > Amin) reduces the storage volume that must be provided in off-lot runoffcontrol facilities (refer to Form 4).

The amount of runoff control volume provided by on-lot and on-road facilities can be calculated asfollows:

� Von-site = [Facility depth (D) x Footprint Area (Aactual)] – [D x Amin] = ____ m3

The total runoff control volume provided by all on-lot and on-road facilities (� Von-site) can then besubtracted from community detention requirements (refer to Form 4).


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Table A - Required Footprint Area (in m2) for Infiltration Facilities(per 1000 m2 of impervious area served by the facility)

Hydraulic Conductivity of On-Site Soils(2) (mm per hour)Effective Depth ofInfiltrationFacility(1) 5 10 25 50 > 100

0.25 m 175 125 75 50 30

0.5 m 140 90 55 40 25

1.0 m 120 70 40 30 20

1.5 m 110 65 35 25 15

2.0 m 100 60 30 20 15

(1) Depths for rainfall capture facilities must be selected based on site-specific characteristics andconstraints. The feasible depth may be governed by physical constraints (e.g. depth to the water table or tobedrock). The effective depth is equal to total depth multiplied by void space, and will depend on facilitytype (see Table A).(2) Based on percolation tests from the development site (ideally carried out under saturated conditions,following periods of extended rainfall). Sizing of rainfall capture facilities should normally be based on theminimum percolation test results from a development site. Tests should be performed at the locations anddepths of proposed infiltration facilities.

Table B - Typical Void Space Storage Values (VS)

Infiltration Facility Type(3) Storage Medium Typical Void Space(VS)

Retention ponds Open 1.0

Bioretention facilities Absorbent soil 0.2

Soakaways (infiltration trenches/pits) Gravel or drain rock 0.33

Infiltration Chambers Sub-surface chambers &surrounding gravel 0.55

(3) Infiltration facilities may be a combination of types. In this case, effective depth of the facility is the sum of totaldepth multiplied by VS, for each layer. For example, a bioretention facility with 0.3 m of ponding depth on top of a1.5 m absorbent soil layer would have effective depth, Deff = [1.5 m x 0.2] + [0.3 m x 1] = 0.6 m.


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Form 4 – Design of Detention Facilities

Runoff Control Criteria: Detain an additional 300 m3 of rainfall per impervious hectare andrelease at 1 Lps per hectare (total site area)

Designing Community Detention FacilitiesThe storage volume that must be provided in community detention storage facilities (e.g. wet or drydetention ponds) is:

� Voff-site = [IAtotal x 300 m3/ha] – [� Von-site] = _____ m3

The rate of release from detention storage is:

� R = Atotal x 1 L/s per ha = _____ L/s

Form 5 – Performance Monitoring Requirements

Target: to provide an accurate picture of how rainfall moves through the stormwater system toenable future evaluation of system performance and optimization of design criteria

) Monitoring within Development SitesThe City will select certain development sites as demonstration projects and develop a comprehensivemonitoring plan for these sites. The costs of installation and continued operation of monitoringequipment will be funded through Development Cost Charges.

The purpose of monitoring within development sites is to evaluate and refine the City’s design criteriaand customize criteria for different zones within Chilliwack. In order to properly evaluate theperformance of a stormwater system, the Water Balance of the development site served by thatsystem must be defined. Therefore, it is important to monitor a representative sample from eachcomponent of the stormwater system, including:

� On-Lot Rainfall Capture Facility monitoring – Monitor water levels and overflow from at least oneon-lot rainfall capture facility.

� for surface facilities - install a compound weir, water level sensor and data logger at the overflowpoint

� for sub-surface facilities – install a piezometer (to measure water level) and data logger

� Road Infiltration/Drainage monitoring – Monitor the road drainage flow from at least one section ofroad. This may include more than one drainage path (e.g. perforated pipe plus catch basinsconnected to a storm sewer).

� install a compound weir, water level sensor, and data logger in a manhole at the downstreamend of the road

� Runoff Control Facility monitoring – Monitor water levels and outflow from detention facilities (e.g.community detention ponds)

� install a compound weir, water level sensor and data logger in the outlet control manhole

B) Monitoring at the Catchment LevelThe City will install streamflow and TSS monitoring stations downstream of catchments where landdevelopment is occurring to verify that development practices are adequately protecting downstreamhydrology and water quality. The costs of installation and continued operation of monitoringequipment will be funded through Development Cost Charges.

Refer to Figure 5-8, in Chapter 5 for illustration of a comprehensive monitoring program.

Chapter Eight

8.1 Determining What is Achievable at the Watershed Scale� The Value of Watershed Retrofit Scenarios� The Need for an ISMP Context

8.2 Watershed Retrofit Case Studies� Indicators of Watershed Restoration� Source Control Scenarios� Case Study #1: McKinney Creek Watershed, Maple Ridge� Case Study #2: Quibble Creek Watershed, Surrey

8.3 Achieving Watershed Protection or Restoration� Changing Development Standards� Facilitating Stormwater Source Control Applications

Watershed Context for Site Design Solutions



MAY 2002


MAY 2002

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8.1 Determining What is Achievable at the Watershed ScaleThe purpose of applying site design solutions is to ultimately achieve benefits (in terms ofwatershed health and/or flood risk management) at the watershed scale.

Determining what is achievable at the watershed scale is key to developing a shared long-term vision for a watershed. This long-term vision then provides a context for all planning,data collection, capital expenditures and regulatory changes.

Section 8.2 presents case studies that show what can be achieved at the watershed scalethrough the application of stormwater source controls.

Section 8.3 illustrates what is needed to achieve the widespread application of source controlsthat are required to achieve significant benefits at the watershed scale.

The Value of Watershed Retrofit ScenariosWatershed retrofit scenarios were modeled using the Water Balance Model (see Chapter 7)for three developed watersheds in the Greater Vancouver Regional District (GVRD). Thepurpose of the watershed modeling was to answer the questions:

� How can implementation of stormwater source controls on all new developments andre-developments over a long time period, on a watershed-wide basis, benefit floodmanagement and urban stream health?

� Are there specific stormwater source controls that work better in theory than others?

The modeling results from two of the GVRD case study watersheds are presented in Section8.2. These results demonstrate that it is achievable to significantly improve and potentiallyrestore watershed health over a 50-year timeline by applying stormwater source controls tore-development projects.

In general, restoring a degraded watershed is more challenging than preserving a healthywatershed. The GVRD case studies demonstrate that watershed restoration is achievablethrough source control (in one of the wettest parts of the province). This also demonstratesthat watershed protection is achievable through stormwater source control.

Drivers for the Watershed Retrofit EvaluationThe Greater Vancouver Region is projected to experience significant population growth overthe next 50 years (possible doubling). This will lead to densification of existing land uses andsome development of existing natural areas, which will increase the volume and rate ofstormwater runoff discharged into watercourses in the GVRD. The increased runoff is likelyto result in:

� the need for upgrades and/or repairs to drainage infrastructure in many parts of theGVRD

� further degradation of aquatic ecosystems in urban watersheds� further water quality deterioration (also a result of population increase)� increased flooding risk to life and property

The effects of climate change are likely to exacerbate these impacts. The amount of fall andwinter rainfall in the GVRD is anticipated to increase over the next 50 years due to climatechange, which will further increase runoff. Climate change is also expected to increase thefrequency of high-intensity rainfall events (cloudbursts), thus increasing the potential forflash flooding.

A key objective of the GVRD’s Effectiveness of Stormwater Source Control report (2002)was to determine how:

� the impacts of increased runoff and more frequent cloudbursts could be avoided byapplying stormwater source controls on future development and re-developmentprojects within the GVRD

� the application of source controls on re-development projects could supportrestoration of aquatic ecosystems and decrease flooding risk over time, thus turning apotential problem (the combination of densification and climate change) into anopportunity (watershed restoration).


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The Need for an ISMP ContextThis chapter provides a broad overview of the potential benefits of source control (at awatershed scale), but does not evaluate source control options in the context of an IntegratedStormwater Management Plan (ISMP) – that is the next step (see Chapter 10). The ISMPprocess will determine what is achievable and affordable in the context of each individualwatershed.

A key objective of any ISMP is to develop a source control strategy that is watershed-specific.

The ISMP process should identify where there is significant aquatic habitat to be protected orrestored, and whether there are drainage problems, such as erosion of ravines or chronicflooding. A more detailed assessment of source control opportunities should focus on areaswhere land use change could cause or exacerbate stormwater-related problems. An ISMPshould evaluate opportunities to mitigate potential negative impacts or to improve conditionsthrough the application of source control.

An analysis of the land use in these catchments will provide an estimate of the expected timeframe for new development or re-development over the next 50 years.

The costs and benefits of implementing source control options in these catchments must beevaluated based on more detailed information on soil conditions, hydrogeology, rainfall,streamflow, drainage infrastructure, land use and site design.


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8.2 Watershed Retrofit Case StudiesThis section summarizes the results of watershed retrofit modeling for two developedwatersheds in the GVRD (see Figure 8-1), including:

� a watershed that is predominantly single family land use (McKinney Creek, MapleRidge), and

� a watershed where re-development to higher density commercial and multiple familyland uses is expected (Quibble Creek, Surrey)

The reference publication for these case study examples is the report Effectiveness ofStormwater Source Control (CH2M Hill Canada, 2002).

Indicators of Watershed RestorationThe watershed retrofit scenarios were evaluated based the following indicators of success:

� Total runoff volume - The primary watershed restoration target is to limit total runoffvolume to 10% (or less) of total rainfall volume. This runoff volume target is basedon the Water Balance of a healthy watershed (see Chapter 6).

� Number of times the natural Mean Annual Flood (MAF) is exceeded – The peak runoffrates from developed areas should only exceed the MAF that occurred under naturalconditions about once per year, on average (more often during wet years). Thisrunoff rate target is based on the hydrology of a healthy watershed (see Chapter 6).

� Peak runoff rate from extreme rainfall events – Reduction of peak runoff rates fromextreme storms (e.g. from a 5-year storm) reduces watercourse erosion and floodingrisk. Specific targets for flood risk management are highly watershed-specific.

The first two indicators show how well stream health is being restored, while the thirdprovides an indication of how well flood risk is being managed over time.

Note that these are simply indicators of potential benefits. A more detailed evaluation ofsource control benefits for a particular watershed must consider the value of aquatic resourcesand the condition of drainage infrastructure throughout the watershed.

Without stormwater source control, land use densification, new development, and climatechange will increase all of these indicators, resulting in watershed degradation.

Quibble CreekWatershed

McKinney CreekWatershed

Figure 8-1 GVRD Case Study Watersheds


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Source Control ScenariosThe following source control scenarios were modeled using the Water Balance Model foreach case study watershed, and evaluated relative to the three indicators of watershedrestoration:

� Scenario 1: Unmitigated – Re-development is assumed to occur according to thestandard practice of land development and stormwater management (i.e. no sourcecontrols applied).

� Scenario 2: Unmitigated with Climate Change – Same as Scenario 1, except thatthe anticipated effect of climate change on rainfall patterns is factored into the futurescenarios.

� Scenario 3: Absorbent Landscaping plus Infiltration Facilities – For all future re-development projects, it is assumed that undeveloped areas are covered by absorbentlandscaping (300 mm soil depth) and infiltration facilities are provided for allimpervious surfaces (infiltration swales on all roads and bioretention facilities on allbuilding lots). The size of infiltration facilities used for each land use type and roadtype were adjusted until the 10% runoff volume target was achieved or until thefeasibility threshold was exceeded.

� Scenario 4: Intensive Green Roofs plus Absorbent Landscaping plus InfiltrationFacilities – Same as Scenario 3, except that all re-developed multiple family andcommercial buildings are designed with intensive green roofs (300 mm of soil depth).The runoff from green roofs is directed to infiltration facilities (sized as described inScenario 3). All re-developed single family homes have impervious roofs connectedto infiltration facilities. Intensive green roofs are not considered feasible for singlefamily land uses.

� Scenario 5: Rainwater Re-use plus Absorbent Landscaping plus InfiltrationFacilities – Same as Scenario 3, except that all re-developed buildings (includingsingle family) incorporate rainwater re-use cisterns (300 m3 of storage per hectare ofrooftop, water re-used for toilets and washing machines). Overflow from the re-usecisterns is directed to infiltration facilities (sized as described in Scenario 3).

The cumulative hydrologic benefits (or impacts) associated with implementing these sourcecontrol scenarios were modeled over a 50-year timeline.

Information and Assumptions Applied to ScenariosThe source control scenarios were modeled based on information and assumptions regarding:

� Land use within the watersheds - Local government staff (from the District ofMaple Ridge and the City of Surrey) provided statistical data on the distribution ofland use types within their respective watersheds. Surrey provided information onboth existing zoning and future Official Community Plan zoning, which provided abasis for quantifying future land use change (densification). The site designcharacteristics for each land use type were estimated based on information on zoningbylaws and development standards (also provided by local government staff).

� Expected timeframe for re-development – For the McKinney Creek watershed, theage of existing development within the watershed was estimated based on discussionwith the local government staff and field investigation. For the Quibble Creekwatershed, the City of Surrey provided data showing the date of servicing forindividual development parcels (a good approximation of building age). A 50-yearre-development cycle was assumed for all watersheds.

� Soil conditions – There was limited soils information available for the case studywatersheds. Conservative assumptions were made regarding the hydraulicconductivity of soils, which resulted in conservative findings regarding what isachievable using infiltration facilities.

� Rainfall - Rainfall data from the GVRD gauges closest to each case study watershedwere used to simulate the performance of the source control scenarios. A year ofcontinuous rainfall data from a very wet year (1999) was used to simulate thescenarios for each watershed.

� Climate change - Climate change scenarios were generated by applying climatechange factors (developed by the Canadian Centre for Climate Modeling andAnalysis) to the rainfall data for each watershed for a very wet year (1999).


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Case Study #1: McKinney Creek Watershed, Maple RidgeLand UseThe majority of land use in the 517 hectare McKinney Creek watershed (about 72%) is singlefamily residential. With the exception of a small amount of housing in the northern portionof the watershed, most of this single family housing is relatively old (pre-1980s) withrelatively low levels of lot coverage (around 30%). The remaining watershed area comprisessome multi-family housing (about 8% of the watershed), some commercial land use alongthe highways (about 6%), and some other land uses (about 14%), including agriculture,schools and community parks.

RainfallHourly rainfall data from GVRD rainfall gauge DM44 in Maple Ridge was used to simulatethe performance of the source control scenarios. Rainfall data from a wet year was used(total annual rainfall = 1811 mm).

Soils InformationThe available soils information included Geologic Survey of Canada mapping, and some soilsmapping that was done in conjunction with a sub-surface drainage assessment (at a fairlycoarse level). Based on this information, a conservative assumption was made that soils inthe watershed have poor to medium hydraulic conductivity (around 6 mm/hr). There waslittle basis for estimating the variability of soil conditions throughout the watershed.

The District of Maple Ridge has reports that indicate the potential for fairly high water tableconditions in a localized region of the watershed. The depth of all infiltration facilities wasreduced to reflect this information.

ResultsThe primary form of re-development that is likely to occur over the 50-year time horizon inthe McKinney Creek watershed is re-development of older (relatively low coverage) singlefamily lots to higher coverage single family lots. This will likely be the result of largerhomes and driveways being placed on existing lots and/or existing large lots being subdividedinto smaller lots.

Figure 8-2 shows the difference in impervious coverage between a typical older single familydevelopment (on the left) and a typical newer single family development (on the right).

Without source control (Scenarios 1 and 2), this re-development is expected to increase totalrunoff volume, peak runoff rates, and the number of times the natural MAF is exceeded (seeFigures 8-3a, 8-3b and 8-3c). The effects of climate change are likely to exacerbate theincrease in runoff volume and rate.

Based on the stated assumptions, the 10% runoff volume target could be achieved withinfiltration facilities and absorbent landscaping (source control Scenario 3) for all residentialland uses, though not for commercial land uses. However, since commercial land usesrepresent a relatively small portion of the total watershed area, the application of infiltrationfacilities and absorbent landscaping could come very close to achieving the 10% runoffvolume target at a watershed scale over the 50-year re-development cycle.

At the watershed scale, there would be little additional benefit gained by adding rainwater re-use or green roofs. The addition of green roofs could significantly improve the reduction inpeak runoff rates from multiple family and commercial land uses. However, since most ofthe watershed is single family, this translates into a relatively small benefit at the watershedscale. Similarly, rainwater re-use would improve the reduction in runoff volume fromcommercial land uses, but this translates into a small benefit at the watershed scale.

Figure 8-2:Re-development impacts in theMcKinney Creek watershed


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Scenario 4 - Green Roofs +Absorbent Landscaping +Infiltration Facilities

Scenario 3 - AbsorbentLandscaping + Infiltration Facilities

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Scenario 2 - Unmitigated Re-development with Climate Change McKinney Creek Watershed Retrofit Scenarios

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Scenario 5 - RainwaterReuse + AbsorbentLandscaping + InfiltrationFacilities

Figure 8-3b

Figure 8-3c

Figure 8-3a


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Case Study #2: Quibble Creek Watershed, SurreyLand UseA substantial portion of land use in the 622 hectare Quibble Creek watershed (about 54%) iscurrently single family. A significant portion of the single family homes are relatively new(post-1980). The remaining watershed area comprises commercial land uses (about 20% ofthe watershed area), some multi-family housing (about 8%), and conservation areas (about18%) that are not likely to develop in the future.

The City of Surrey’s Official Community Plan calls for significant densification in theQuibble Creek watershed. About two-thirds of the existing single family housing in thewatershed is expected to re-develop into multiple family land uses (a range of densities). Theamount of commercial land is not likely to increase substantially, but existing local andcommunity commercial land uses are expected to re-develop as higher-density town centrecommercial.

RainfallHourly rainfall data from GVRD rainfall gauge SU56 in North Surrey was used to simulatethe performance of the source control scenarios. Rainfall data from a wet year was used(total rainfall = 1733 mm).

Soils InformationThe only soils information available for the watershed was the Geologic Survey of Canadasoils mapping (1:50,000 scale). This mapping shows about half of the watershed to be highconductivity soils and the other half to be low conductivity soils. Based on this information,a conservative assumption was made that soils have poor hydraulic conductivity (around 2.5mm/hr). Aside from the coarse level GSC mapping, there was no basis for estimating thevariability of soil conditions throughout the watershed.

ResultsThe primary impact of densification in the Quibble Creek watershed is likely to result fromthe re-development of single family land uses to multi-family land uses with higherimpervious coverage (see Figure 8-4). Commercial densification also increases imperviouscoverage but to a lesser extent (even local commercial land uses have relatively high levels ofimpervious coverage).

Without source control (Scenarios 1 and 2), densification and the effects of climate changeare expected to increase total runoff volume, peak runoff rates, and the number of times thenatural MAF is exceeded (as shown in Figures 8-5a, 8-5b and 8-5c on the following page).

The 10% runoff volume target could be achieved with infiltration facilities and absorbentlandscaping for all land uses except those with greater than about 80% impervious coverage(includes the highest density multi-family land uses and nearly all commercial land uses). Atthe watershed scale, the application of absorbent landscaping and infiltration facilities (i.e.Scenario 3) could reduce runoff volume to about 20% of total rainfall. In order to achieve the10% target, it would be necessary to apply rainwater re-use to the high coverage land uses(i.e. Scenario 5).

Green roofs and rainwater re-use would have more significant runoff reduction benefits forthe Quibble Creek watershed than for the McKinney Creek watershed (Case Study #1)because high coverage land uses (high density multi-family and commercial) represent alarger portion of the total watershed area. The benefits of rainwater re-use are mostsignificant in terms of reducing runoff volume. The benefit of green roofs are mostsignificant in terms of reducing peak runoff rates from extreme rainfall events.

Since much of the development in the Quibble Creek watershed is relatively new, theopportunity to apply source control to re-development projects is likely limited in the shortterm (over the next 10 years).

Figure 8-4:Projected densification inQuibble Creek watershed


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Quibble Creek Watershed Retrofit ScenariosReduction in Frequency of Runoff Events Exceeding Natural MAF

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Scenario 1 - Unmitigated Re-development

Scenario 2 - Unmitigated Re-development with ClimateChange

Figure 8-5c

Figure 8-5a

Figure 8-5b


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8.3 Achieving Watershed Protection or RestorationWidespread application of stormwater source control is needed to protect or restorewatershed health. This will require changes to the standard practice of land development andstormwater management.

The details of these changes will vary from one watershed to the next. Watershed-specificsource control strategies should be developed through the ISMP process (see Chapter 10)based on an assessment of watershed-specific opportunities and constraints.

The core objective is to identify options to change the way that land is developed and re-developed, so that people, property and natural systems can be better protected; and overtime, stormwater infrastructure can be managed more efficiently and watersheds can beprotected or restored.

Changing Development StandardsAn ISMP may identify the need for changes to development standards and regulations inorder to implement a watershed-specific source control strategy. The level of support fromthe public and from all levels of government, as well as the ability of the developmentcommunity to adapt to new standards, will set the pace of change and influence the pace ofISMP implementation.

This support can only happen if there is a broad understanding among all players, thedevelopment community in particular and public in general, about the changes in standardpractices - why they are needed, what they are, and how they can be practicallyaccomplished.

Facilitating Stormwater Source Control ApplicationsThe first large-scale applications of stormwater source controls and supporting policies maybe implemented as demonstration projects. Local governments (independently orcollectively) will need to take the lead in implementing and monitoring these initialdemonstration projects (e.g. public works projects, neighbourhood concept plans, progressiveISMPs).

Local government leadership is important for demonstrating to developers, the communityand senior government regulators that proposed actions at the site level are both effective andaffordable. This will build support for the regulatory, professional and industry changes thatwill enable the realization of long-term stormwater infrastructure planning and management.

Monitoring demonstration projects provides the foundation for adaptive management. Thegoal is to learn from experience and constantly improve land development and stormwatermanagement practices. Hydrologic monitoring is fundamental to adaptive management,since it is the hydrologic indicators that provide the information needed to improve the waywe develop land and manage stormwater at the site level.

In order to build and maintain trust between local governments, landowners, developers andsenior government agencies, the rules of adaptive management must be established at theISMP stage. These rules must define requirements and consequences of monitoring. Inmany instances, either prior to or concurrent with the first demonstration projects, there willbe a need to change current standards and administrative processes to accommodate thesenew standards. The following steps will facilitate this process of change:

� Step 1 - Establish an enabling regulatory framework – Make regulatory changesthat will facilitate the approval process for development and re-development projectsthat capture rainfall at the source for infiltration, evapotranspiration and/or re-use.

� Step 2 - Ensure that new design standards reflect local conditions - Through theimplementation and monitoring of demonstration projects, establish the designoptions for source control that will be most effective in the context of site-specificconditions (i.e. soils, precipitation, planned land use, etc).

� Step 3 - Adopt a collaborative approach to change – Consult with citizens and thedevelopment industry to determine:

� preferred design options for stormwater source control� appropriate implementation strategies for regulatory change� appropriate financing strategies for rainfall capture and runoff control


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� Step 4 - Incorporate the most effective and acceptable design options intoengineering standards - Revisions to engineering standards should reflect localconditions as well as the preferences of the community and the development industry.Although new engineering standards for source controls can be incorporated into therelevant development regulations (Subdivision Bylaws, Building Bylaws, ZoningBylaws, Development Permit Guidelines), it is also possible that standards could beperformance-based, leaving the determination of appropriate source control strategiesto the proponent as part of their development application.

� Step 5 - Make the details of new design standards readily available - Create atechnical manual of options for on-lot stormwater source control, including detailsand specifications of design standards, and make it available on-line.

� Step 6 - Facilitate procurement of materials needed to implement new designstandards - Implement a bulk purchase/re-sale program that makes it easy andaffordable for developers to obtain the specialty products needed to implementstormwater source control. Also, provide a cheap source of material for absorbentsoils through a local government composting program.

� Step 7 - Build support through education - Implement education programs toinform city staff, the development community and the general public about the needfor changes in development practices and how to implement them.

In summary, these seven initiatives form the basis for a developing an action plan (seeChapter 9) which provides a framework for removing barriers and reaching the targetcondition for a watershed over a period of years.

Chapter Nine

9.1 Overview of ISMPs� Objectives of an ISMP� Elements of the ISMP Process� Layered Approach to Developing an ISMP� ISMP Technical Products� Political Commitment to the ISMP Process� Case Study Example: GVRD Template for ISMPs

9.2 Process for Developing and Implementing an ISMP� Case Study Example: Brunette Basin Plan and Stoney Creek ISMP

9.3 Step #1: Secure Political Interest and Support� Framework for ISMP Process� Communicating Relevant Information for Elected Officials� Leadership and Inter-Departmental Commitment� Stakeholder Involvement

9.4 Step #2: Frame the Watershed Problems and Opportunities� Applying a Knowledge-Based Approach� Making Use of Available Information� Case Study Examples: Creating a Picture of Stream Habitat Conditions

Developing and Implementing an IntegratedStormwater Management Plan (ISMP)


9.5 Step #3: Develop Objectives and Alternative Scenarios� Developing a Shared Vision� Identify Alternatives and Make Choices� Case Study Example: Scenarios for Stoney Creek ISMP� Case Study Example: Evaluate Scenarios and Make Choices� Using Performance Targets to Quantify Watershed Objectives� Modeling Alternative Scenarios

9.6 Step #4: Collect Meaningful Data and Refine Scenarios� Be Strategic When Investing In Data Collection� Data on Soils and Groundwater� Data on Drainage Facilities� Data on Fish and their Habitats� Water Quality Data� Sources of Data

9.7 Step #5: Evaluate Alternatives and Develop Component Plans� Habitat Enhancement Plan� Flood Risk Mitigation Plan� Land Development Action Plan� Adding the Dimension of Time

9.8 Step #6: Develop An Implementation Program� Financial Plan and Implementation Program

9.9 Step #7: Refine Through Adaptive Management� Defining the Rules of Adaptive Management� Adaptive Management Roles and Responsibilities� Types of Monitoring� The Role of Effectiveness Monitoring� Managing Drainage from an Ecological Perspective

9.10 Synopsis of the Seven-Step Process for ISMP Development and Implementation� Build the Vision, Create a Legacy

STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIAPART C – MOVING FROM PLANNING TO ACTION

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9.1 Overview of ISMPsThe focus of Part B was on developing integrated solutions at the site level, where the sourceof stream degradation and flooding problems can be eliminated. The purpose of this chapteris to:

� Show how these site level solutions fit in to a larger watershed context, and arecomplemented by a range of other watershed protection and flood risk managementtools.

� Provide a framework for developing an ISMP. This framework is adapted from arange of BC case study experiences.

In general, an ISMP process must address the following fundamental question:

� How can the ecological values of stream corridors and receiving waters be protectedand/or enhanced, and drainage-related problems prevented, while at the same timefacilitating land development and/or redevelopment?

Objectives of an ISMPThe objectives of an ISMP will be watershed-specific, but will generally encompass thefollowing:

� Drainage Objectives - Alleviate existing and/or potential drainage, erosion,and flooding concerns.

� Stream Protection Objectives - Protect and/or restore stream health,including riparian and aquatic habitat.

� Water Quality Objectives - Remediate existing and/or potential water qualityproblems.

The ISMP focus is on the integration of stormwater management and land use planning. AnISMP is an integral component of a local government’s land development and growthmanagement strategy because upstream activities (land use change) have downstreamconsequences (flood risk and environmental risk).

Elements of the ISMP ProcessThis chapter presents a process for developing an ISMP for a watershed and its constituentdrainage catchments. Through this process, watershed stakeholders collectively answer thequestions listed below and illustrated as Figure 9-1:

� “What do we have?” - understanding the watershed issues

� “What do we want?” - setting achievable performance targets

� “How do we get there?” - developing an ISMP implementation program

"What do we have?"

"What do we want?"

"How do we get there?"

Figure 9-1


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Layered Approach to Developing an ISMPFigure 9-2 conceptualizes the building blocks that are the essence of an integrated approachto stormwater management. It was originally developed to guide an ISMP process for theCity of Kelowna.

Figure 9-2 also illustrates how the bridge is built between environmental goals (as defined bycommunity expectations and legislative initiatives) and a stormwater management and streamstewardship strategy (as defined by an ISMP). This involves a layered approach:

� First Layer – Identify the stormwater-related objectives for a watershed (e.g.protection of aquatic resources, protection of life and property, protection ofwater quality). These objectives define what the ISMP is striving to achieve.

� Second Layer – Develop strategies to achieve the watershed objectives.This includes setting performance targets to guide selection of site designsolutions.

� Third Layer – Implement appropriate site design solutions (e.g. sourcecontrols) for achieving performance targets that suit local objectives andconditions.

To select appropriate stormwater management strategies and site design solutions, it is firstnecessary to identify the resources to be protected, the threats to those resources, and thealternative management strategies for resource protection. The foundation for this approachis found in the At-Risk Methodology presented in Chapter 5.

ISMP Technical ProductsAn ISMP includes three core deliverables or ‘technical products’ – an inventory, componentplans, and an implementation program - as shown in the table part of Figure 9-2. Thesetechnical products were introduced in Chapter 4.

The distribution of effort among the three products should be balanced. Often effort isconcentrated on the inventory phase, and not enough effort is invested in the elements of animplementation program. The best plan, without a sound implementation program, can resultin watershed conditions getting worse with time rather than better.

The remainder of this chapter presents the process for developing and implementing an ISMPfor either a watershed or its component drainage catchments.

Political Commitment to the ISMP ProcessIf site level solutions are to successfully fit into a larger watershed context, political will andcommitment are essential inputs at two critical points in the ISMP development process:

� Launching the ISMP Process – Unless there is a political buy-in to dothings differently, the process will not be effective.

� Implementing the ISMP Action Plan - Political will is crucial ifthere is to be a move from planning to action.

Integrated solutions transcend technical analyses. This chapter discusses how to securepolitical support and commitment to first develop and then implement an ISMP. Lookingahead, Chapter 11 elaborates on the ingredients for building consensus and creating change.

Community Expectations and Legislative InitiativesCommunity expectations and legislative initiatives provide the driving force for politicalaction to launch the ISMP process. Community expectations are reflected in both an OfficialCommunity Plan and a Liquid Waste Management Plan. This is the first building block asshown in Figure 9-2.


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ISMP DELIVERABLE SCOPE OF DELIVERABLE

An inventory of thephysical and biological

systems

� streams, rivers, and drainage systems� wetlands, ponds and lakes� infiltration areas and aquifers� land use information� flooding and erosion problem areas� water quality problems

Component plans toprotect key resources,

resolve identified problems,and accommodate

development

� plan for integrating appropriate source controls with land development,including a description of any required regulatory changes

� plan for improvements to drainage systems and stream reaches� plan for ongoing data collection and monitoring� cost estimates for all planned actions

An implementationprogram

� administration� projects, phasing and budgets� financing mechanisms� community education� maintenance activities, standards and schedules� performance monitoringFigure 9-2


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Case Study Example: GVRD Template for ISMPsThe Greater Vancouver Regional District (GVRD) has developed a Terms of ReferenceTemplate for Integrated Stormwater Management Planning (2002) to provide a standardizedprocess that includes all of the key stormwater components. These are listed in Table 9-1,and are categorized in terms of three disciplines – engineering, planning and environmental.The work effort is organized as four phases:

� Information Gathering (15 tasks)� Analysis (9 tasks)� Alternatives (6 tasks)� ISMP (5 tasks)

A municipality can decide which components are applicable, and establish the level of effortrequired based on risk and local conditions. Not all of the components may be relevant for agiven watershed or drainage catchment.

*Legend of Codes for ISMP Components

E1 = Engineering itemP = Planning itemE2 = Environmental itemS = Stakeholder/Public ProcessI = Integration of all disciplines

Table 9-1: ISMP Components (from GVRD Template)

ISMP Component Code*1 Establish Framework I2 Mapping/Information Gathering I� Stakeholder/Public Notification & Consultation S3 Hydrometric Data Collection E14 Drainage System Inventory E15 Hydrogeology/Geotechnical Assessment E16 Land Use Information P7 Agricultural Lands P8 Recreation Opportunities & Public Access P9 Biophysical Inventory E2

10 Riparian Corridor Assessment E211 Wildlife Assessment E212 Benthic Community Sampling E213 Water Quality Analysis E214 Baseplan Mapping I

Info

rma

tio

n G

ath

eri

ng

15 Existing Stormwater Program I16 Hydrological Analysis (Tool 1) E117 Hydraulic Analysis (Tool 2) E118 Channel Erosion E119 Agricultural-Upland/Lowland Analysis E120 Natural Hazard Assessment E121 Land Use Sensitivity Analysis P22 Recreation & Public Access Analysis P23 Environmental Parameters E2

An

aly

sis

24 Ecological Health Analysis (Tool 3) E225 Flood/Erosion Management Alternatives E126 Land Use Alternatives P27 Stormwater Management Alternatives E228 Water Quality Alternatives E229 Evaluate Alternatives I30 Stormwater Program IA

lte

rna

tiv

es

� Stakeholder/Public Consultation S31 ISMP I32 Implementation Strategy I33 Integrate with Other Municipal Master Plans I34 Develop Adaptive Management Program I35 Draft/Final Report I

ISM

P

� Stakeholder/Public Consultation S


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9.2 Process for Developing and Implementing an ISMPFigure 9-3 illustrates a seven-step process for developing and implementing an ISMP. Theobjective is to reach the target condition over time. This process is based on a provenapproach to decision making for complex issues. This process underpinned the four ISMPcase studies introduced in Table 1-1.

The first six steps ultimately lead to implementation of integrated solutions for a watershed.These steps are described in Sections 9.3 to 9.8. Overcoming barriers in order to get fromStep #5 to Step #6 is described in the context of moving from planning to action.

In Step #7, the ISMP process is revisited in a greater level of detail to validate and refine theintegrated solutions. Step #7 will involve successive cycles of adaptive management overtime. This step is discussed in Section 9.9.

Case Study Example: Brunette Basin Plan and the Stoney Creek ISMPThe Stoney Creek ISMP established a British Columbia precedent for application of all stepsin the seven-step process to move from planning at the watershed scale to action at the sitelevel. This was a pilot project that was completed in 1999 as part of the GVRD’s BrunetteBasin Plan (reference: Table 1-1). Success at each level has been accomplished through aworking session process that resulted in a shared vision of what is achievable, both in theshort-term and over the long-term.

Develop a Shared Watershed VisionThe Brunette River is an inter-municipal waterway that is managed by the Greater VancouverRegion District. It receives runoff from five cities: Vancouver, Burnaby, New Westminster,Coquitlam, and Port Moody.

The Brunette River Basin Plan was developed through an inter-municipal pilot process forconsensus-based watershed planning in the Greater Vancouver Region. All fivemunicipalities agreed to the vision, goals and objectives for catchments within the Basin. To

determine how to achieve the shared watershed vision, the Stoney Creek catchment wasselected as a pilot program for ISMP development.

Selecting an At-Risk Drainage CatchmentStoney Creek was selected for three reasons: it has the highest value aquatic resources; theseresources are at risk due to pending residential development in the Burnaby Mountainheadwaters; plus it has an active and proactive streamkeeper group. The Stoney Creek pilotprogram was also directed by an inter-municipal and inter-agency Steering Committee.

The purpose of the pilot program was to test the principles of a watershed-based approach tointegrating stormwater and riparian corridor management. The Stoney Creek process resultedin a philosophy and hydrologic criteria for watershed protection and restoration over a 50-year timeline. By consulting the streamkeeper group and applying their expert knowledge, anaquatic habitat rating was established for each creek reach. The critical reaches droveselection of the plan elements for stormwater management.

Protect the Natural Water Balance at the Site LevelA high-density urban community for 10,000 people is being built at the top of BurnabyMountain, the headwaters of Stoney Creek, over a 20-year period. Hence, this is where earlyaction has been focused to blend policy, science and site design. The resulting BurnabyMountain Watercourse and Stormwater Management Plan (2002) is a pilot project forstormwater volume reduction at the source. The Plan has been developed under the umbrellaof an inter-agency advisory committee. The Plan:

� translates the Stoney Creek vision and hydrologic criteria into performancetargets and design criteria that are being applied at the neighbourhood level

� translates the performance targets and criteria into specific stormwatermanagement and site design practices

The performance of the Burnaby Mountain stormwater management system will bemonitored as development proceeds. In this way, stormwater management and site designpractices can be improved for future development within the Brunette Basin, and elsewhere.


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Step Description and Scope

1 Secure Political Interest and Support� Inter-departmental & inter-agency steering committee� Political and public support� Stakeholder focus groups

2 Frame the Watershed Problems and Opportunities� Assemble existing information� Identify and prioritize problems (knowledge-based approach)

3 Develop Objectives and Alternative Scenarios� Establish desired levels of environmental protection and other

objectives� Set appropriate performance targets� Model alternative scenarios for achieving targets

4 Collect Meaningful Data and Refine Scenarios� Collect data needed to:

� refine scenario models� evaluate effectiveness and affordability� e.g. hydrometric data, soils data

5 Evaluate Alternatives & Develop ISMP Component Plans� Land Development Action Plan� Habitat Enhancement Plan� Flood Risk Mitigation Plan

6 Develop an Implementation Program� Finance and implement ISMP actions

7 Refine Through Adaptive Management� Define adaptive management rules, roles and responsibilities� Constantly improve integrated solutions Figure 9-3


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9.3 Step #1: Secure Political Interest and SupportAn ISMP process starts with a high-level political commitment to protecting property, waterquality and aquatic habitat. This policy commitment is made through an over-arching OCPand/or LWMP. Step #1 in the actual ISMP process is to convert high-level policy statementsinto concrete action so that there will be a flow of funding for the ISMP process.

To accomplish this objective requires a different level of political support, especially whenthere are multiple watersheds and the financial commitment is multi-year. Without politicalsupport for funding, there will be no ISMP process. Once funding is assured, however, a keyto a successful outcome is that there be a commitment by all stakeholders to make the ISMPprocess work.

Framework for ISMP ProcessBefore elected officials can be expected to commit to a long-term investment in an ISMPprocess for multiple watersheds, local government managers must be able to provide a clearand convincing case that answers four questions:

� Why do it?� What will it cost?� What are the benefits?� Why should this take priority over other community needs?

These questions are best addressed through front-end development of an over-arching orframework document that:

� Defines a drainage planning philosophy� Formulates a set of supporting policy statements� Establishes design criteria to achieve the policies

This approach provides elected officials with an informed basis for making the decision tofund and proceed with the first ISMP (Step #2). The purpose of the over-arching document isto demonstrate to elected officials that there has been stakeholder input, that stakeholdershave endorsed the process, and that stakeholder input is reflected in the policy content.

Case Study Example: City of Chilliwack Surface Water Management ManualThe City of Chilliwack has developed a Policy and Design Criteria Manual for SurfaceWater Management (2002) that serves two purposes:

� At the Watershed Scale - Provides a comprehensive framework that will guidethe development of individual ISMPs over a multi-year period.

� At the Neighbourhood and Site Scales - Provides land developers with specificdirection in undertaking the stormwater component of sustainable urban design.

The Manual was developed and vetted through an inter-departmental and inter-agencyprocess that also included community participation. It took nine months to complete, andculminated with an interactive session with Chilliwack City Council.The Manual presents key information that elected officials, City staff, and land developersneed in order to understand and implement the City’s approach to stormwater management.The Manual includes a five-year Action Plan for removing barriers and undertaking ISMPs.

Case Study Example: Regional District of Nanaimo Action PlanChapters 4 and 5 described how the stormwater component of the Regional District ofNanaimo’s (RDN) Liquid Waste Management Plan was developed through a roundtableprocess. This resulted in a five-year Action Plan for gradual phase-in of stormwatermanagement.

At the end of the five-year period, the RDN will have developed a clear understanding ofappropriate stormwater management approaches that are customized to the local environmentand are acceptable the development community.

The objective of the RDN is to take small steps that build community and political supportfor undertaking ISMPs. It is proposed that a pilot ISMP be completed in year four.

Time-Frame for Launching an ISMP ProcessThe RDN timeframe is consistent with the experience of Chilliwack and other communities.It typically takes 3 to 5 years of sustained effort for local government to generate themomentum needed to launch a new program. In part, this reflects the budget cycle. When aneed is first identified, it may take a year or two to obtain initial funding. There are oftendelays in funding subsequent steps in the process.


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Communicating Relevant Information to Elected OfficialsSecuring political approval and commitment to proceed to Step#2 requires that the need foraction be communicated in clear and concise terms. Presented below is an example of asingle page synopsis of the supporting rationale for a Resolution by Council to adopt anAction Plan that will guide City of Chilliwack staff for the next five-year period.

Case Study Example: City of Chilliwack Staff Report� Manage the Complete Spectrum of Rainfall Events – The City’s approach to

stormwater management is evolving, from a reactive approach that only dealtwith the consequences of extreme events, to one that is proactive in managing all170 rainfall events that occur in a year. The objective is to control runoff volumeso that watersheds behave as though they have less than 10% impervious area.

Reducing runoff volume at the source – where the rain falls - is the key toprotecting property, habitat and water quality.

� Five-Year Action Plan for Integration of Stormwater Management andLand Use Planning – In 2000, Council accepted a Process Flowchart andTimeline for moving forward with master drainage planning. The Manual is amilestone in that process. It identifies and organizes the actions required over thenext five years to achieve the City’s stormwater management objectives.

Implementation of regulatory change should proceed on a phased-in basis, withISMPs providing a mechanism to study, test and adapt proposed regulations tosuit the range of needs and conditions in Chilliwack.

� Submission Requirements for Land Development Projects – To provideclarity and conciseness regarding the City’s expectations and requirements forsubdivision design, the Manual defines the technical information that landdevelopers must submit to the City in order to obtain development approvals.The Manual also includes Design Guidelines that illustrate how to comply withperformance targets for stormwater source control, detention and conveyance.

Having a comprehensive checklist will help proponents think through thedrainage details of project implementation, and will ensure consistency in theway information is presented for review and evaluation by the City.

Leadership and Inter-Departmental CommitmentLeadership is established through the formation of a Steering Committee that has inter-departmental representation. Also, there must be a champion within local government (referto Chapter 11) to provide the energy and organizational drive needed to move the ISMPprocess through the various steps.

The integration of disciplines and departmental objectives must be the beginning andfoundation of any ISMP. Only then should each discipline focus on its specific analyticalskills and tools.

The objective is to benefit from the synergies that result from brainstorming and the sharingof interdisciplinary perspectives. Thus, it is important to create an atmosphere that isconducive to free thinking and open discussion.

Too often the reverse is used where disciplines work independently, and at best integrationbecomes merely a lateral process or something added at the end to appease stakeholders.

Stakeholder InvolvementBecause of the implications for land use planning and aquatic habitat, senior governmentagencies and other affected stakeholders need to be represented in the ISMP developmentprocess. Chapter 11 elaborates on how to involve stakeholders in a Focus Group so that theycan contribute to development of integrated solutions.

Looking ahead to Chapter 11, the stakeholder involvement process is described as the secondtrack in a ‘Two-Track Approach’ because technical analysis feeds into working sessions withthe Steering Committee and Focus Group.


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9.4 Step #2: Frame the Watershed Problems andOpportunities

Step #2 is critical. This involves application of an interdisciplinary roundtable process (referback to Chapter 5) to identify and rank the problems and opportunities in a watershed.Sufficient time must be invested at this stage to ensure that there is a clear understanding ofthe problems to be solved. This understanding will then guide the rest of the ISMP process.

All too often, technical people go directly to Step #4 (Collect Data) without first asking whatthey are trying to accomplish, and why. As a result, they solve the wrong problem, and thenwonder why elected officials and/or the public takes issue with the proposed solution.

Applying a Knowledge-Based ApproachIt is important to identify where problems are in relation to areas where future land usechange is likely (new development or re-development), because land use change can:

� create or exacerbate stormwater-related problems (e.g. degrade aquatic resourcesor increase flooding risk)

� present opportunities to restore stream health, improve water quality, or reducedrainage-related problems through the application of source controls

The knowledge-based approach described in Chapter 5 should be applied to determine whatthe existing and/or potential problems and issues are in a watershed, and the level of concernrelated to these problems and issues.

Existing knowledge and information about a watershed should be adequate to determinewhere in the watershed there are general indicators of existing or potential problems, such as:

� flood hazards� stream channel erosion� aquatic habitat degradation� water quality deterioration

The roundtable approach relies on the knowledge of local residents and key experts (from theplanning, ecology and engineering disciplines), combined with a local government’s existinginformation on land use, aquatic resources and drainage systems.

Making Use of Available InformationAvailable information can and should be used to provide a better understanding of thewatershed. The following information is useful in helping to define the watershed issues andframe the problems:

� Watershed Base Map - the first building block� Watershed Issues Summary - where and what are the identified problems� Sensitive Ecosystem Inventory - what is to be protected� Land Use Map - what are the existing and future generators of runoff� Drainage System Inventory - how the conveyance system functions� Concurrent Rainfall and Streamflow Data - how the watershed responds

to rainfall� Soils and Groundwater Maps – where might infiltration be feasible

The foregoing are the core deliverables resulting from Step #2. This set of graphics providesa picture of the watershed. Visual presentation helps develop a common understandingamong ISMP participants. Section 9.5 explains why this is so.

All available information should be assembled at this stage to help frame the problems, butfurther investment in data collection should not be made at this stage. Once watershedobjectives and catchment-specific performance targets are established (see Step #3), theinvestment in data collection can be directed where it will be most useful and effective. Datacollection is discussed in depth in Step #4.

Broad-Brush Ranking of IssuesIn Step #2, the approach is broad-brush. The objective is to create understanding and anintuitive feel for conditions in the watershed. This will then guide follow-up investigationsthat achieve greater levels of detail where it is required.

An outcome of Step #2 should be a preliminary ranking of watershed issues. This rankingwould reflect a generalized assessment of questions such as: Is flooding the dominantconcern? Or is it aquatic habitat degradation? Is water quality a real or perceived problem?Where can existing and/or potential problems be turned into opportunities?


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Case Study Examples: Creating a Picture of Stream Habitat ConditionsThe evolving science of stormwater management has broadened the traditional engineeringapproach to one that integrates flooding and aquatic habitat concerns. Whereas flooding anderosion problems are normally obvious to all, habitat concerns can be subtle in nature.Hence, assessing aquatic habitat at an overview level is a key part of framing the problems ina watershed. This helps to focus subsequent effort.

The Bear Creek and Stoney Creek case studies introduced in Table 1-1 resulted indevelopment of a five-task process for creating a reach-by-reach picture of aquatic habitatconditions. This process applies the knowledge-based approach described in Chapter 5, andgoes to another layer of detail in assessing conditions reach-by-reach. The desired outcome isa mapping tool that serves two purposes - planning and communication.

� Task #1 - Develop an Ecosystem Overview: Review all existing biophysicalinformation for stream corridors.

� Task #2 – Identify and Fill Critical Data Gaps: Fill any critical information gapswith a reconnaissance inspection of specific locations or reaches.

� Task #3 – Create a Planning Tool: Prepare an overview map of the stream thatidentifies spawning and rearing habitat and highlights aquatic habitat concernsrelated to readily apparent sedimentation and erosion, barriers to fish movementand point sources of pollution.

� Task #4 - Prioritize Ecosystem Values: Convene a workshop for individualswith practical, hands-on experience in the watershed to refine the stream map andbuild consensus on stream corridor and/or aquatic habitat values and threats.

� Task #5 - Integrate Ecosystem Values: Analyze and integrate the habitat andfisheries constraints with the engineering requirements and a land use map thatbreaks the stream into reaches for stormwater planning.

Task #4 is pivotal as it provides the foundation for the habitat component of an ISMP. Tobuild local government commitment and secure financial support for habitat protection and/orenhancement initiatives, it is first necessary to demonstrate what is to be protected, and why.

9.5 Step #3: Develop Objectives and Alternative ScenariosStep #3 involves further application of the interdisciplinary roundtable process to:

� determine which problems and/or opportunities are priorities for action� establish objectives for dealing with these priority problems/opportunities� develop alternative scenarios for achieving the objectives

Developing a common understanding among participants in the ISMP process is key todeveloping a shared vision of what is desirable, practical and achievable.

Developing a Shared VisionPeople typically learn best in one of three ways: either by seeing, by hearing or by doing.Hence, it is important to use a variety of communication techniques to ensure clarity ofunderstanding. Looking ahead, Chapter 11 elaborates on this topic. In general, a commonunderstanding is achieved in a workshop setting by:

� illustrating concepts through the use of graphics

� guiding individuals to blend concepts with their own experience

The graphic presented on Figure 9-4 translates scientific findings on the impacts of land usechange into a decision making tool for stormwater goals and objectives. It illustrates theconsequences for stream corridor ecology of various attitudes towards stormwatermanagement.

Figure 9-4 was at the heart of the stakeholder visioning process for all four ISMP case studiesintroduced in Table 1-1. Participants were provided with clear visual choices regarding adesired ISMP outcome.

To reach consensus on a shared vision of what is desirable and achievable for watershedprotection, ISMP participants need a picture of what a stream corridor could and/or shouldlook like. Figure 9-4 fulfils this need. The visioning process boils down to whether or not astream corridor will have a functioning aquatic ecosystem.


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Figure 9-4


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Identify Alternatives and Make ChoicesFigure 9-4 captures the evolution of drainage planning philosophy over the decades forwatersheds that include some prior development. It provides a framework for definingstrategic objectives and identifying management practices for achieving those objectives.

Figure 9-4 provides a starting point for an interdisciplinary roundtable to make choices andagree on a guiding philosophy for integrated stormwater management for specific watersheds.It can also be employed to assess whether technical solutions are environmentally andpolitically acceptable. The choices can be considered to lie on a spectrum of:

(Allow to) Worsen �------------"Hold the Line" ----------------------�Improve

The process of determining an appropriate shared vision balances what is desired (or ideal)with what is technically feasible, affordable and politically palatable.

Integration of Aquatic Habitat Condition AssessmentThe results of the five-task aquatic habitat condition assessment in Step #2 provide both aframe of reference and a starting point for scenario development in Step #3. The reach-by-reach picture enables ISMP participants to ask two questions:

� Where are we now?� Where do we wish to be in future?

In general, priority effort should generally be directed where the best habitat is threatened bypending or potential land use change.

Starting Point for an Action PlanFor developed watersheds, Level 3 (from Figure 9-4) would be the likely starting point for anaction plan, with the objective of moving from left to right over time (i.e. to improveconditions).

For an undeveloped watershed, the starting point would likely be Level 5, with the objectiveof ‘holding the line’ to preserve and protect existing habitat values in the short term, withrestoration of aquatic habitat over the long term.

Case Study Example: Scenarios for Stoney Creek ISMPBased on Figure 9-4, the alternative watershed visions listed below were defined for StoneyCreek:

� SCENARIO A - Status Quo Strategy for StreamManagement (Level 2)Maintain the status quo for local government decision making arounddevelopment practices. Existing regulations and procedures would continue,and habitat values would continue their present downward trend.

� SCENARIO B - Hold the Line and Accommodate GrowthStrategy for Stream Management (Level 3)Sustain existing environmental conditions as development and re-developmentproceeds, with associated additional program requirements and financial costs.

� SCENARIO C - Enhance Aquatic Conditions andAccommodate Growth Strategy for Stream Management(Level 4)Enhance existing aquatic environmental conditions, but at substantial additionalcost for regional facilities and increased requirements for on-site facilities tomanage stormwater from new development and redevelopment.

The application of these scenarios to make decisions is discussed next. These scenariosprovided the basis for Resolutions by all three City Councils that embraced Scenario B as the20-year vision, and Scenario C as the 50-year vision.


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Case Study Example: Evaluate Scenarios and Make ChoicesTable 9-2 is the Stoney Creek example of how to apply a decision making matrix forevaluating alternative scenarios. The decision criteria are the management objectives. Todecide which level of environmental protection is preferred, the decision maker mustdetermine how well each scenario achieves each objective and balance the trade-offs andconflicts.

With the matrix, each criterion can be considered for each scenario and the results can bevisualized, compared and recorded. In a workshop setting, roundtable participants canevaluate and discuss each alternative and select a preferred approach.

Because data are often limited, and in view of the complexities of dealing with naturalsystems, each decision maker has to rely in part on his/her own informed, professionaljudgement to evaluate the alternatives.

Adding the Dimension of TimeChange takes time. What is not achievable in the next five years may be quite achievableover fifty years. Integration of stormwater management with land use planning involves atimeline. General time-related objectives can be defined as follows:

� 20-Year Vision (Preservation) – Develop policies and implementdemonstration projects that show how to succeed in achieving streampreservation (i.e. ‘hold the line’), thereby building support for the 50-year visionto improve watershed and stream conditions.

� 50-Year Vision (Improvement) – Continue to implement changes inland use and regulation that mitigate changes in hydrology at the source (i.e.improve conditions), thereby enabling watershed protection/restoration andlasting stream improvement.

Ongoing monitoring and assessment of progress towards a long-term vision will improve theunderstanding of how to blend policy, science and site design to achieve the shared vision forproperty, water quality and habitat protection. Building on initial successes, localgovernments may well decide to advance the schedule and strive for improvement within the20-year horizon.

Table 9-2 Decision Criteria to Select Strategies for Stream ManagementHOW WELL DOES EACH SCENARIO

ACHIEVE EACH OBJECTIVE?�OBJECTIVES ORDECISION CRITERIA SCENARIO A

(LEVEL 2 )SCENARIO B

(LEVEL 3)SCENARIO C

(LEVEL 4 )As Established by the

Brunette Basin Task Group

IMPORTANCE?�

STATUS QUO,CONTINUEDDECLINES INFISH

HOLD THE LINE,SUSTAIN TROUTAND HATCHERYSALMON

ENHANCEHABITAT,SUSTAINWILD SALMON

1. Protect or enhancebiodiversity

very important low medium high

2. Protect or enhanceaquatic habitat*

very important low medium high

3. Protect or enhanceterrestrial habitat

moderate importance low medium high

4. Enhance recreationopportunities

moderate importance low medium high

5. Minimize health andsafety impacts

very important high high high

6. Minimizetotal costs

very important high(no change inexisting costs)

medium(increased costs)

low(high cost)

7. Minimize propertydamage

very important medium high high

8. Increase scientificand managementunderstanding

least important medium high high

9. Increase opportunityfor public learning

least important medium high high

�

�

Three judgmental choices are provided for rating each objective: very important, moderate importance, and least important.Three judgmental choices are provided for rating each scenario: low, medium and high.


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Using Performance Targets to Quantify Watershed ObjectivesPerformance targets provide a quantifiable way of measuring success in protecting (orrestoring) a watershed, and for identifying what needs to be done to achieve a givenenvironmental protection objective.

� Desired protection objectives for significant stream reaches should be translatedinto performance targets for the catchments draining into those reaches. Forexample, to maintain or restore the health of a stream reach, an appropriateperformance target would be to limit the volume of runoff from land uses in thedrainage catchment to 10% or less of total rainfall volume.

� For catchments upstream of drainage ‘hot spots’ (e.g. chronic flooding locations),a more appropriate performance target may be to reduce peak runoff rates fromlarge rainfall events (e.g. 5-year storms).

� Other performance targets relating to the preservation/restoration of significantnatural features (e.g. riparian forests, wetlands), measurement of stream health(e.g. B-IBI), protection/improvement of water quality, or instream enhancements(e.g. for habitat or fish passage) should also be established.

A key principle is to establish performance targets that relate directly to the watershedobjectives. Refer back to Chapter 6 for further guidance on setting performance targets.

The selected targets should also be monitored over time to ensure that the ISMP is achievingthe desired results. Refer to Section 9.9 for more detail on this topic.

Setting Performance TargetsTo establish realistic performance targets for a given watershed, an ISMP must answerquestions such as those introduced in Chapter 6 and reiterated below:

� What is the existing level of annual runoff volume? What percentage of totalannual rainfall volume does it represent? What is the existing Mean AnnualFlood (MAF)?

� What are acceptable levels of runoff volume and rate in terms of flood risk andenvironmental risk? What are the consequences of increased or decreased flowsrelated to land development? Are these consequences acceptable?

� What actions are needed to avoid flooding or environmental consequences?

� How can the necessary actions be staged over time?

� Are the targets to maintain 10% runoff volume and maintain the natural MAFnecessary or achievable over time? If not, what levels are?

Modeling Alternative ScenariosScenario modeling can be used to assess a range of performance targets, and evaluate optionsfor achieving these targets.

Scenario modeling involves consideration of the complete spectrum of rainfall events thattypically occur in a year. (Refer back to Chapter 6 for further details regarding the threetiers.) An integrated approach to managing these events comprises three components:

� retain the small events (Tier A) at the source,� detain the large events (Tier B) in detention facilities� safely convey the extreme events (Tier C)

Relationship of Rainfall Spectrum to Watershed ObjectivesThe balance between the above three components depends on the watershed objectives.

� Stream protection/restoration objectives would likely govern scenarios thatemphasize source control (e.g. infiltration, rainwater re-use), along with otherpossible options, such as riparian corridor protection.

� Flood management objectives would likely govern scenarios that place moreemphasis on detention and conveyance.

The key is to determine which scenario or blend of scenarios has the best ‘fit’ to address arange of watershed objectives.

A key aspect of scenario development will be to consider what can be done at the site level toretain the small events, given constraints such as soil conditions, hydrogeology, topographyand land use. Further data collection may be required to assess the feasibility of achievingperformance targets (see Step #4).


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Modeling HierarchyA computer model is a decision support tool. A model can help evaluate alternativescenarios, but it does not make decisions. Sometimes there is a tendency to over-emphasizethe value of modeling. The reliability of model output depends on the quality of the inputdata, and especially on the judgement of the modeler in making critical assumptions.

A fundamental principle is that the level and/or detail of modeling should reflect theinformation needed by decision makers to make an informed decision. The modeler mustalways take a step back and ask three key questions:

1. Why is the model being built?2. How will the model be applied?3. What problems will the model help us solve?

Figure 9-5 illustrates the four main levels (or applications) of drainage modeling. Movingdown the pyramid reflects an increasing level of detail, and hence investment of resources.

At this stage of the ISMP process, modeling should be at a strategic (i.e. conceptual oroverview) level to provide basic information to support the decision making process.

Modeling tools take on added importance once the focus shifts to the functional planning anddesign of proposed stormwater management facilities. More data is required at this level ofmodeling.

Data Requirements for Strategic Level Scenario ModelingContinuous rainfall data (in time increments of one hour or less) is the key data requirementfor scenario modeling. Ideally, site-specific rainfall data should be used, but even data from alocation with similar rainfall characteristics can be used at this stage.

At this strategic level of modeling, the other model inputs (e.g. regarding land use and soilconditions) should be estimated based on the best available information (assembled in Step#2). Where there is high degree of uncertainty regarding certain parameters, a range ofassumptions may be tested, and data collection efforts can then be targeted to refine theseassumptions (see Step #4).

The appropriate type of modeling will depend on the characteristics of the scenarios beingmodeled, as discussed on the following page.

Policy EvaluationPolicy EvaluationStrategic DecisionsStrategic DecisionsMaster PlansMaster Plans

Detailed DesignDetailed Design

OperationsOperations

StrategicStrategic

Functional Functional PlanningPlanning

Modeling Hierarchy

Figure 9-5


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Types of Modeling: Single Event versus Continuous SimulationThere are two types of modeling: ‘single event’ and ‘continuous simulation’. Single eventtypically means a storm duration up to 24 hours. Continuous simulation typically covers ayear or a multi-year period, with time-steps up to 1 hour. Their respective applications aresummarized as follows:

� Single Event Modeling – acceptable for most applications of Tier C flood riskmanagement

� Continuous Simulation Modeling – required for Tier A rainfall capture, Tier B runoffcontrol, and some applications of Tier C flood risk management

For both types of modeling, measured rainfall data (rather than artificial ‘design storms’)should be used as input data. Refer back to Chapter 6 for further discussion on the threerainfall tiers.

Continuous Simulation for Source Control (Tier A) and Detention (Tier B)

The distinction between Tier A and Tier B modeling is that Tier A requires volume-basedthinking, whereas Tier B involves flow-based thinking. Conventional modeling packages areflow-based, and thus most appropriate for modeling detention (Tier B) and conveyance (TierC) scenarios.

Models may be hydrologic (i.e. simulate runoff response), hydraulic (i.e. perform flowrouting functions), or both. A selection of flow-based models is provided below for referencepurposes. The appropriate model type depends on the scenario being modeled.

Model Name Does it have ContinuousSimulation Capabilities?

Is it a Hydrologic and/orHydraulic Model?

HEC-1 No Hydrologic

HEC-RAS No Hydraulic

HYDSYS No Both

OTTHYMO No Hydrologic

QUALHYMO Yes Hydrologic

HSPF Yes Hydrologic

SWMM Yes Both

MOUSE Yes Both

Note that the level of effort and amount data required to apply these models is highlyvariable. Some of these models require a high level effort, which may not be suitable forscenario modeling applications at the strategic level. The GVRD ISMP Template providesfurther details on these models.

Because Tier A simulation is volume-based, it is described as Water Balance modeling (referback to Chapter 7 for further details). Since the focus of stormwater source control is onrunoff volume reduction, Water Balance Modeling is most appropriate for source controlscenarios. The Water Balance Model (WBM) is an example application (refer back toChapter 7 for details).


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Source Control Scenario ModelingWhereas the use of conveyance and detention are relatively well understood stormwatermanagement strategies, the use of source control is less well-known. Discussion amongISMP participants is likely to focus on whether source controls are effective or practical inthe context of watershed-specific conditions.

Generating source control scenarios through Water Balance modeling can be a critical tool ininforming this discussion (refer back to both Chapters 7 and 8).

Model scenarios can provide guidance for selecting source control options to achievecatchment-specific performance targets. Further data collection should focus on collectingthe information needed to determine whether these options are achievable (see Step #4). Forexample, if infiltration is identified as an option for achieving performance targets in aparticular drainage catchment, a key information need would be to determine soil conditionsin that catchment.

Flood Management Scenario ModelingThe primary purpose of modeling for flood management purposes (i.e. Tier C) is to assess theconveyance capacity of drainage facilities installed at stream crossings. The level ofpreciseness in quantifying design flows is not critical because rated capacity is not thegoverning consideration.

Physical adequacy normally governs the acceptability of a drainage installation (refer back toChapter 6). Hence, the real purpose in comparing design flows to rated capacities is toprovide a relative measure of the degree of risk. This comparison helps elected officialsmake decisions to invest in drainage facility upgrades and/or replacement.

For certain flood management scenarios, continuous simulation modeling would be moreappropriate. For example, continuous simulation would be needed to provide an idea of theextent and duration of flooding over an extended period of time under different detentionand/or flow conveyance scenarios.


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9.6 Step #4: Collect Meaningful Data and RefineScenarios

Step #4 is to collect the additional data that may be needed to evaluate the effectiveness,feasibility and affordability of implementing the scenarios identified in Step #3 for meetingwatershed objectives.

This step may involve collecting site-specific data to refine the assumptions of the scenariomodels generated in Step #3 (e.g. site-specific data on soils or drainage system components).

Be Strategic When Investing in Data CollectionThe level and/or detail of data collection should reflect the information needed by thedecision maker to make an informed decision. This principle is framed by these threequestions:

� Why do we need the data?� How will the data be applied?� What problems will the data help us solve?

The impacts of changes in land use are generally understood. At this point, the investment indata collection needs to be strategic. We know that restoring the natural Water Balance andhydrology is required to address the source of stormwater-related problems. Data collectionshould focus on improving understanding of how to do so in the context of local conditions.

Before investing in data collection, there needs to be a clear understanding of themethodology to ensure that data collection is done right. Consistency and rigour areimportant to allow the data to be used as a baseline for comparison with future data.

Concurrent Rainfall and Streamflow DataHaving reliable rainfall and streamflow data is the key to a performance-based approach toISMP development, implementation and effectiveness monitoring.

The minimum requirements are a streamflow station at the drainage outlet of watersheds orcatchments of concern, and a strategically located rainfall station.

Concurrent and continuous records of rainfall and streamflow data provide a picture of thecharacteristic rainfall-runoff response of a neighbourhood, a drainage catchment or awatershed. Having a picture creates understanding. Understanding is required for twoconditions in particular:

� ‘rainfall-runoff response’ during wet weather periods� ‘runoff decline’ during dry weather periods

The latter is key to baseflow analysis. Baseflow availability is likely to be the limiting factorfor fish survival in small streams during dry weather periods.

Rainfall and streamflow data play a key role in an adaptive management program (see Step#7 and also refer back to Chapter 6). Monitoring the change in rainfall-runoff response asland development progresses in a catchment will indicate the effectiveness of site designsolutions.

Concurrent rainfall and streamflow data is also needed to calibrate and verify computermodels. This is key to refining the scenarios developed in Step #3.

Streamflow Data from Undeveloped CatchmentsMonitoring streamflow in undeveloped catchments (i.e. under natural conditions) providesvaluable information because it defines the target hydrograph. The key objective for thedesign and operation of stormwater systems is to replicate this target hydrograph as closely aspossible in catchments where development is occurring.

Streamflow data from undeveloped catchments also provide the best basis for establishingrelease rates for detention facilities (refer back to Chapter 6). Monitoring also provides abaseline for evaluating any future changes in hydrology due to development in thesecatchments.


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Data on Soils and GroundwaterSoil and groundwater conditions govern the feasibility and affordability of using infiltrationfacilities to meet catchment-specific performance targets for runoff volume or rate reduction.

If not already available, soils information should be collected in catchments where infiltrationis identified as an option for achieving stream protection and/or flood managementobjectives. This will enable a more detailed assessment of what is actually achievable inthese catchments.

It is also important to collect basic groundwater information to identify areas where thegroundwater table is very high, since infiltration is not likely feasible in these areas.

Refer back to Chapters 6 for details regarding the importance of soils information in settingcatchment-specific performance targets. Refer back to Chapter 7 for details on therelationship between soils and infiltration performance.

Data on Drainage FacilitiesScenario modeling may identify flood management concerns relating to certain drainagesystem components. Data collection should then focus on characterizing these criticaldrainage system components and evaluating the effectiveness of improvement options.

For example, if the conveyance capacity of a particular culvert installation is identified as ahigh risk flooding location, data collection may focus on determining the effectiveness ofoptions for improving physical and/or hydraulic acceptability of that culvert.

Data on Fish and their HabitatsWhere watershed objectives focus on the protection and/or restoration of fish and theirhabitats, there may be a need to collect additional data to define the value of these resourcesand evaluate options for their protection or restoration.

For example, if restoration of a critical stream reach is established as an objective, detailedsurveys of this reach would likely be required to evaluate restoration options.

Water Quality DataIf surface water or groundwater pollution is identified as a key issue in a catchment, theremay be a need to collect water quality data in order to provide a better understanding of thetypes and sources of pollution. This would become important for evaluating options tomanage the sources of water quality problems.

For example, high nutrient loading in watercourses may indicate the need to manage runoffquality from upstream agricultural areas.

Monitoring turbidity (and correlating with TSS) can provide a good indicator of changes inwater quality and watercourse erosion rates over time. This can play an important role inevaluating the effectiveness of integrated solutions that are implemented in a watershed (referback to Chapter 6).

Also, performance targets can be established based on total suspended solids (TSS) loading,using natural loading rates as a baseline. Note that TSS targets are closely related to runoffvolume targets (increase in runoff volume is the primary cause of watercourse erosion).

Sources of DataData can typically be obtained by contacting the federal and provincial agencies listed below:

� Rainfall – from the Atmospheric Environment Service (Environment Canada)� Streamflow – either from the Water Survey of Canada (Environment Canada) or

the provincial Ministry of Water, Land and Air Protection (MWLAP)� Species and Habitats of Concern – either from Fisheries and Oceans Canada or

the Environmental Stewardship Division of MWALP� Water Quality - from the Environmental Protection Division of MWALP


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9.7 Step #5: Evaluate Alternatives andDevelop Component Plans

Once watershed objectives have been established, alternative scenarios for achieving thoseobjectives have been generated, and the data needed to evaluate the effectiveness of thesescenarios has been collected, the next step is to evaluate the alternatives and make decisions.

These decisions will provide the basis for developing plans for habitat enhancement, floodrisk mitigation and relevant land development actions. These are all related components ofan ISMP, as shown in Figure 9-6. These component plans are described in this section.

The fourth component is a financial and implementation program (see Step #6), which isessential for moving from planning to action.

Habitat Enhancement PlanThe Habitat Enhancement Plan should identify:

� key wetlands or sensitive ecosystem areas needing protection

� riparian setback objectives

� schematic alignment for creek relocations, with corresponding riparianrestoration and land requirements

� streamside and instream complexing features to be incorporated

� location and description of barriers to fish passage, and prescriptions to removebarriers where advisable

A companion report would provide cost estimates, land acquisition costs, logical phasing andlogistics of the planned habitat improvements. It should outline a monitoring andmaintenance program that addresses jurisdiction and ownership of stream corridors, andrequirements for agency approvals.

Figure 9-6


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Flood Risk Mitigation PlanThe Flood Risk Mitigation Plan should identify:

� required stormwater storage facilities

� proposed split between storage budgets in community detention facilities andprivate developments

� type and distribution of stormwater infiltration and storage facilities

� flow paths for major events

� piped sections, or high-flow pipe diversion works

� conceptual cross-sections of major stream diversions

A companion report would provide a description of the elements and cost estimates for landacquisition and capital works, suitable for use in development cost charge (DCC) bylaws andcapital works plans.

Land Development Action PlanA Land Development Action Plan should illustrate the relationship between the proposedhabitat enhancement and flood mitigation works and existing and proposed land use in thewatershed. Recommended changes to land use designations should be highlighted forconsideration in Neighbourhood Plans and the Official Community Plan.

Location and routing of flood control works, stream relocations and riparian leave stripsshould be developed within a strategy for land acquisition or regulatory protection. The LandDevelopment Action Plan should show the location of required lands and outline a strategy toachieve their protection over the long-term.

The Land Development Action Plan should also identify the distribution of stormwatersource control use in the watershed. Some source controls may be targeted to only part of thewatershed (e.g. infiltration only in certain soil conditions). Other source controls may vary inapplication by zoning (e.g. green roofs only on commercial or multiple family buildings).

Adding the Dimension of TimeChanges take time. What is not achievable over the next five years may be quite achievableover a twenty-year or fifty-year timeline. Action plans to integrate stormwater managementwith land use planning should be framed in terms of long-term visions and time-relatedobjectives (e.g. what do we want to achieve over the next 5, 20 and 50 years). Refer back toSection 9.5 for further discussion of planning horizons.


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9.8 Step #6: Develop an Implementation ProgramStep #6 is essential for moving from planning to action, yet many planning processes neverget to this step. Without an implementation program and financial plan, watershed objectiveswill not be achieved.

Financial Plan and Implementation ProgramThe purpose of an ISMP is to identify the risks, what needs to be done to manage the risks,who should be responsible, and lay out a general timeline for implementation.

The Financial Plan and Implementation Program should therefore outline how the landacquisition and capital financing of the elements can be achieved. Tools might includenegotiations during zoning changes, land exchange, density bonuses, adjustment of existingDCCs or other means. Strategies will be specific to the properties in question.

In addition to capital financing, the regulatory framework is another component ofimplementation to be used in balance with public awareness and capital works programs.

There many questions related to regulatory change that must be resolved, including:

� What is the role of various regulatory tools (e.g. zoning negotiations, developmentpermits for protection of the natural environmental, ecosystems and biodiversity, treeprotection bylaws, watercourse protection bylaws, engineering standards andspecifications)?

� How can regulatory tools work together, without overlap or excessive red tape?

Chapter 11 provides guidance regarding the types of regulatory changes that may be neededto achieve stormwater management objectives.

Recommended Bylaw ApproachA key objective of the ISMP process is to create a recommended bylaw approach. Thiswould define the bylaw that each stormwater source control or policy is to be implementedthrough, and the relationship between bylaws. The product would be a point form outline ofeach proposed bylaw change. The outline should be relatively specific, and should address:

� Enabling legislation� Principles behind the bylaw change� Key bylaw requirements� Key definitions needed� Key illustrations or engineering details needed� Key filter and exemption clauses� Key application information requirements� Enforcement options

This product should provide clear direction for subsequent work by separate assignment towrite and provide legal review of the actual bylaw changes. Land use regulation shouldreflect a pragmatic approach that is based on these guiding principles:

� Principle #1 - Recognize the body of existing local bylaws, and identify howthey can be adapted to suit new objectives.

� Principle #2 - Create the simplest possible regulatory system. Watch out foroverlap or conflicting bylaws. Try to reduce the number of permits required.

� Principle #3 - Understand that bylaws will only succeed if the solid majorityof the public supports them.

The last principle underscores the importance of public awareness programs that provide thepublic and the development community with the information they need in order to decidewhether to support new regulations.


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9.9 Step #7: Refine Through Adaptive ManagementStep #7 is key to resolving stakeholder uncertainty associated with changes in standardpractice. This objective is achieved through an adaptive management framework asillustrated by Figure 9-7. This will be ongoing through time.

Monitoring and evaluating the performance of demonstration projects will provideconfidence in new approaches. It will also provide the basis for optimizing stormwatersystem design to reduce costs while still achieving defined goals for protecting downstreamproperty, aquatic habitat and receiving water quality (refer back to Chapter 6).

Defining the Rules of Adaptive ManagementAn ISMP implementation plan must define:

� Early Actions - the integrated stormwater management solutions to beimplemented in priority (at-risk) catchments

� Rules of Adaptive Management – a clear set of rules that definemonitoring requirements and consequences to allow for improving integratedsolutions over time

Build and Maintain TrustIn order to build and maintain trust between local governments, landowners, developers andsenior government agencies, the following questions must be answered at the plandevelopment stage:

� What needs to be monitored?

� How will monitoring results:

a) define better stormwater management and development practices?b) lead to changes in development standards and regulations?

The adaptive management framework presented in Chapter 6 provides a starting point forestablishing a set of rules that answer the above questions. This must be a collaborativeprocess, so that the rules are understood and supported by all stakeholders.

Desired OutcomesA clearly understood and widely supported set of adaptive management rules will:

� Enable landowners and developers to make long-term land use and investmentdecisions with more confidence.

� Provide senior government agencies with regulatory certainty as new approachesare tested and refined.

� Ensure that the investments of local governments (both staff and financialresources) will lead to constant improvement.

Figure 9-7


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Adaptive Management Roles and ResponsibilitiesAn implementation plan must clearly define who is responsible for monitoring what, andestablish regular intervals (e.g. every year) for working sessions to review monitoring results.These working sessions are critical to the ongoing process of change, because this is wheredecisions will be made regarding what to change and how these changes will be made.

Local governments may need to take the lead in implementing and monitoring the initialdemonstration projects (e.g. on public works projects). Local government leadership isimportant for demonstrating to developers, landowners and senior government regulators thatproposed actions at the site level are both effective and affordable. This will build support forregulatory changes that enable or require these site level actions.

Stewardship groups also have a role to play in monitoring the catchment and watershed scaleeffectiveness of new land development practices.

Types of MonitoringThe following types of monitoring should all be included in a comprehensive adaptivemanagement program.

� Effectiveness Monitoring – Determines the extent to which the completedactions have achieved the management objectives (for example, monitor thevolume and frequency of overflow from an on-site facility and compare with theperformance targets).

� Compliance Monitoring – Identifies whether or not the implementingparties have completed the actions they agreed to complete in the planning phase(for example, confirm that developers are incorporating properly sized on-sitestorage and infiltration facilities).

� Validation Monitoring – Measures the extent to which completion of theobjectives (actions) has been successful at achieving the goal (for example,monitor annual watershed runoff volume and compare with the performancetarget established for runoff volume reduction).

Effectiveness monitoring is the key to learning from experience and constantly improvingland development and stormwater management practices.

The Role of Effectiveness MonitoringChapter 6 included a discussion on performance monitoring in the section about optimizationof stormwater system design. Chapter 6 also introduced the need for performance monitoringat different scales. This section elaborates on that discussion.

Proper assessment of the effectiveness of site design practices in a watershed context requiresmonitoring at three scales:

� Site Level - Monitor Volume and Frequency of Overflow fromIndividual FacilitiesThe performance of individual rainfall capture and runoff control facilities mustbe monitored to determine if targets for runoff volume reduction and rate controlare being met.

� Neighbourhood Level - Monitor the Change in Rainfall-RunoffResponse from Development AreasIt is important to monitor flow at the drainage outlet (e.g. outfall to a stream) of adevelopment area serving an integrated network of rainfall capture and runoffcontrol facilities. This will enable an assessment of how well this integratedsystem achieves the performance target for volume reduction.

� Catchment Level - Monitor Early Warning Indicators of StreamHealthIt is important to determine how well actions at the site level are maintaining orrestoring a healthy catchment. This can be accomplished by monitoring thefollowing indicators:

� Water Balance - streamflow at the downstream end of the catchment� Water quality - turbidity and total suspended solids (TSS)� Biophysical - Benthic Index of Biological Integrity (B-IBI)


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Managing Drainage from an Ecological PerspectiveThis section elaborates on indicators that can be used to provide a warning system regardingthe impacts of human actions on the environmental health of stream corridors so thatcorrective action can be taken when they are required.

The governing consideration is that indicators accurately represent the environmental state ofboth the surface drainage function and the ecological function of the receiving waters.

Elements of an Integrated Program for Monitoring Stream HealthIn recent years stormwater managers have recognized the need for a stream health monitoringprogram that is sensitive to changes in hydrology and habitat. The need arose becausetraditional chemical and physical monitoring did not produce the type of information neededto understand the overall environmental health of a stream corridor and manage drainagefrom an ecological perspective.

A comprehensive approach combines simplified chemical and physical monitoring withannual monitoring of physical changes to habitat and a biological index of benthic organisms.

An Integrated Monitoring Program would comprise ambient biological monitoring,continuous rainfall and streamflow recording, some chemical and habitat measurements, andpossible microbiological monitoring to allow the identification of fecal coliform sources.

Description of Ambient MonitoringA baseline ambient monitoring program would comprise Benthic Index of BiologicalIntegrity (B-IBI) scores at selected sites, plus concurrent field measurements of conductivityand temperature, plus physical measurements of stream and habitat elements.

For chemical parameters, conductivity has the best correlation with urban impacts. Also, itcan be measured inexpensively in the field. TSS and zinc also have good correlation, butprovide little additional information over that provided by conductivity alone.

9.10 Synopsis of the Seven-Step Process for ISMPDevelopment and Implementation

Table 9-3 provides a synopsis of the seven-step process. For each step the scope, desiredoutcome, and deliverables are summarized. The overall aim of this process is to achievehealthier urban watersheds over time.

Build the Vision, Create a LegacyA shared long-term vision is needed to focus the effort that will create a legacy. This visionprovides a context for all planning, data collection, sensitivity analyses, capital expendituresand regulatory changes. Prioritizing goals and actions (ideally through consensus) provides aroad map for moving towards a target condition by identifying:

� the interconnected nature of goals, values and expectations� risks and opportunities� what needs to be done to manage the risks and achieve the opportunities� who should be responsible� a general timeline for implementation

This framework addresses the goal of identifying options to change the way that land isdeveloped and re-developed, so that people, property and natural systems can be betterprotected and over time, infrastructure can be managed more efficiently and watersheds canbecome healthier.


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Step Scope Outcome Deliverable

1 Secure Political Interest and Support � Define a guiding philosophy� Formulate supporting policies� Establish design criteria to achieve policies

� Document 1 - Policy and Design Criteria Manual

2 Frame the Watershed Problems and Opportunities(Apply the Knowledge-Based Approach)� Land Use Working Session� Drainage Working Session� Ecology Working Session� Interdisciplinary Roundtable Session

� Identify resources to be protected� Establish an order of priority for plan development at the sub-watershed scale

� Document 2 – Understanding the Watershed

� Watershed Base Map� Watershed Issues Summary� Sensitive Ecosystem Inventory� Land Use Map� Drainage System Inventory� Soils and Groundwater Map

3 Develop Objectives and Alternative Scenarios� Flood Management Scenario Modeling� Source Control Scenario Modeling

� Identify inadequate drainage facilities� Establish a customized performance target for each sub-watershed

� Document 3 – Results of Flood Management Scenario Modeling� Document 4 – Results of Source Control Scenario Modeling

4 Collect Meaningful Data and Refine Scenarios� Concurrent Rainfall and Streamflow Data� Data on Soils and Groundwater� Water Quality Data� Data on Fish and Their Habitats

� Identify gaps� Supplement existing programs

� Document 5 – Data Collection Framework

5 Evaluate Alternatives and Develop Component Plans � Make decisions � Document 6 – Flood Risk Mitigation Plan� Document 7 – Habitat Enhancement Plan� Document 8 – Land Development Action Plan

6 Develop an Implementation Program � Consolidate supporting documents� Develop financial plan� Create a recommended bylaw approach

� Document 9 - Implementation Report

7 Refine Through Adaptive Management � Establish rules of adaptive management� Implement comprehensive monitoring program

� Document 10 - Performance Evaluation Plan

Table 9-3 Synopsis of the Seven-Step Process for ISMP Development and Implementation

Chapter Ten

10.1 Framing the Question� Taxpayer Willingness to Pay� Taxpayer Ability to Pay

10.2 Making Choices� Dealing with Complexity� Measuring Risk

10.3 Who Pays?� Division of Responsibility� Cost Sharing Between Developers and Local Government� Supporting Innovation and Leadership� Responsibility for Operation and Maintenance

10.4 Sources of Funding� Overview

10.5 Setting up a Stormwater Utility� Legislative Authority� Scope of a Utility� Benefits of a Utility� Revenue and Billing

10.6 Regional Approach� Cross-Jurisdictional Funding of Watershed Action Plans� Other British Columbia Experience

Funding an Integrated StormwaterManagement Plan (ISMP)



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10.1 Framing the QuestionIn developing and funding a stormwater program, local governments are faced with thechallenge of balancing risks of flooding and environmental degradation against communitywillingness to pay. This chapter provides strategies to address this challenge.

Since the primary source of revenue for local government is property taxes, stormwaterprogram budgets will be largely governed by taxpayer ‘willingness to pay’ and taxpayer‘ability to pay’. Since local governments always face competing priorities, a thoroughconsideration of risks and consequences becomes critical when establishing spendingpriorities.

A related issue is due diligence; once a risk is identified, local government has aresponsibility and an obligation to address that risk. As introduced in Chapter 1, anIntegrated Stormwater Management Plan (ISMP) provides a framework for addressing riskand moving towards a target condition by identifying:

� the risks

� what needs to be done to manage the risks

� who should be responsible

� a general timeline for implementation

Taxpayer Willingness to PayWillingness to pay is refers to the level of increase in taxation rate that taxpayers are preparedto accept in order to pay for a particular service, in this case, stormwater planning andmanagement. Willingness to pay will be governed by taxpayers’ understanding of what is atrisk. Local governments must be proactive in explaining the potential consequences (both interms of flooding and property damage and habitat and species loss) of delaying or avoidingimplementation of stormwater plans, to ensure that taxpayer willingness to pay is balancedagainst risk.

Taxpayer Ability to PayWillingness to pay is linked directly to ability to pay. Hence, it is important to understand thecost implications of what it means to embrace a stream stewardship philosophy.Fundamental questions that will need to be answered when building public understanding andsupport for a funding plan are:

� What level of aquatic resource protection is achievable and sustainable, andwhich elements of stream stewardship are applicable?

� What is the local government liability and financial exposure in accepting seniorgovernment directives for protection/enhancement of aquatic habitat?

� Will the societal benefits justify the costs incurred? (i.e. is there a payback?)

Addressing these questions upfront will enable a local government to judge what level ofstream stewardship is achievable and sustainable at an affordable cost.


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10.2 Making ChoicesThe extent of a stormwater funding program will be influenced by willingness to pay, level ofprotection versus expenditures, ability to raise revenue, and level of investment versus riskreduction.

Potential sources of revenue for local government are explained in the next section. Thesesources include general revenue, development cost charges (DCCs), specified area charges,stormwater utilities and senior government grants.

Dealing with ComplexityTwo distinct core concepts that must be integrated in any stormwater funding program aresummarized below:

� Expenditures versus Revenue - There is a cost to taxpayers toconstruct facilities that protect property and sustain the natural environment. Aslocal government takes on more responsibility, funding must be provided to fulfilthe commitments that have been made. This is a comparatively straightforwardrelationship to quantify.

� Willingness to Pay versus Environmental Consequences -The less the public is willing to invest in property and habitat protection, thegreater the likelihood that problems will worsen. Conversely, more investmentshould improve the situation, provided the investment is strategic and addressesthe sources of problems. This is a much more complex relationship to quantifybecause it involves value judgements.

Both components implicitly provide local government with flexibility to match willingness topay to an affordable level of protection. The third dimension is time, as discussed in Chapter9. Thinking in terms of a long-term time horizon provides the opportunity to achievecumulative net benefits over time.

Measuring RiskThe less that the public is willing to pay, the higher the risk there will be of adverseenvironmental consequences. This is a concept that local governments are only justbeginning to consider. Deciding not to invest in stormwater management does notnecessarily equate to cost savings, since there is a cost associated with the status quo if itmeans watershed conditions will deteriorate. Deteriorating watershed conditions result inflood damage and channel stabilization costs, as well as habitat loss and water qualityimpairment.

Underlying the issue of risk is the question of liability and due diligence. For example, if alocal government knows that either the status quo or inaction will result in consequences thatcan be foreseen, they can be held legally liable for those consequences. On the other hand, ifa local government demonstrates due diligence in developing a plan to forestall thoseconsequences, this should normally relieve the liability. It then becomes a matter ofmatching the timing of plan implementation to ability to pay.


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10.3 Who Pays?The tiered approach is one of the cornerstones of this Guidebook. It provides a logical andappropriate basis for assigning responsibilities and determining who pays for what.

Division of ResponsibilityTable 10-1 suggests a division of responsibility (i.e. who pays) for implementing the threestormwater management ‘tiers’ - retain, detain and convey. The issue of who should pay forstormwater management is directly related to the following question:

� Are stormwater-related problems (habitat degradation, flooding) the result of pastdevelopment, future development, or some combination?

For new development in an undisturbed watershed or catchment, the land developer would beexpected to bear the cost for managing the complete spectrum of rainfall events. For urbanretrofit scenarios where there are existing problems (degraded habitat, flooding) as a result ofpast development, local governments (i.e. existing landowners and taxpayers) would typicallybe expected to bear much of the cost. In most situations some level of cost sharing betweendevelopers and local governments will be appropriate.

For Table 10-1 to be applicable to a regional district, the regional district would first have toapply for drainage authority.

Cost Sharing Between Developers and Local GovernmentRegardless of the initial land use in a particular catchment, new development or re-development projects should be responsible for managing Tier A events using rainfall capturestrategies on private property. The responsibility for new developments should also includedesigning roads in new subdivisions to be self-mitigating (i.e. provide rainfall capture andrunoff control) for Tier A events.

Local government would clearly be responsible for retrofitting existing roads as part of along-term watershed or drainage catchment restoration strategy.

New developments and local government should each contribute a proportionate share of thecost for providing runoff control for Tier B events and flood risk management for Tier Cevents, depending on the relative impacts of existing and future development.

Table 10-1 Who Pays for Stormwater Management Infrastructure?

Land Development ScenarioComponent ofIntegrated Strategyfor Managing theComplete Rainfall

Spectrum

New subdivisionwithin a mainlyundeveloped

catchment

New subdivision within a partially

developed catchment

Re-developmentwithin a fully

developedcatchment

Rainfall Capture for thesmall Tier A Events

(on-lot retention)

developers/landowners




(on-street retention)developers

developers for roadswithin subdivision

local government forexisting roads

local government(i.e. municipalities)

Runoff Control for thelarge Tier B Events

(detention)developers*

cost sharing betweendevelopers and

local government onan area basis*

local government*(i.e. municipalities)

Flood Risk Managementfor Tier C Events

(contain and convey)developers

cost sharing betweendevelopers and

local government (i.e. municipalities)

local government (i.e. municipalities)

* Runoff control targets can either be met by providing larger rainfall capture facilities (Tier A) or byproviding community detention facilities. For re-development scenarios this choice can have implications for who pays. The more on-lot storage thatdevelopers/landowners provide, the less local government funded community storage will be required.


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Supporting Innovation and LeadershipInnovation and leadership is being provided at the local government level. But movingtowards a new standard practice for suburban design requires a considerable investment ofstaff time and financial resources to successfully implement and monitor demonstrationprojects.

During the transition period, it seems reasonable to suggest that senior governments shouldsupport innovation and leadership by funding demonstration projects. This is the mosteffective way for senior governments to limit the risk and liability associated with beinginnovative. The lessons learned will benefit all local governments. Therefore, it seemsreasonable that the leaders be supported in their efforts to implement change.

Responsibility for Operation and MaintenanceTable 10-2 parallels the previous table and summarizes who is responsible for operating andmaintaining each tier of stormwater infrastructure.

Under the present system, subdivision developers are responsible for infrastructure integrityfor a set period of time (typically one year) before a municipality formally takes possession ofthe completed works. Property owners have responsibility for maintenance of any drainageworks that are located on private property.

During the transition period to a new standard practice, local governments have the option toextend the performance monitoring period for rainfall capture and runoff control facilities, forexample, from one year to three years. A precedent is the Burnaby Mountain sustainablecommunity that is being built by Simon Fraser University.

Table 10-2 Who Operates and Maintains Stormwater Management Infrastructure?

Land Development ScenarioComponent ofIntegrated Strategyfor Managing theComplete Rainfall

Spectrum

New subdivisionwithin a mainlyundeveloped

catchment

New subdivision within a partially

developed catchment

Re-developmentwithin a fully

developedcatchment


(on-lot retention)

property owners property owners property owners


(on-street retention)




Runoff Control for thelarge Tier B Events

(detention)




Flood Risk Managementfor Tier C Events

(contain and convey)





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10.4 Sources of FundingFive sources of funding that are potentially available to municipalities to pay forimplementation of ISMPs are listed as follows:

� General Revenue – from all taxpayers� Development Cost Charges – from land developers� Specified Area Charge – from local neighbourhoods� Stormwater Utility – from all property owners� Senior Governments – via grant programs

Regional districts are limited in their ability to raise money. Funding must be tied to aspecific function that is delegated by the municipalities; that function can only be assigned byreferendum.

OverviewFrom a funding perspective, the focus of local government is on how to pay for runoff controlfor Tier B events and flood risk management for Tier C events. This applies mainly to ascenario where municipalities must finance the retrofitting of a catchment with detention andconveyance facilities. This also applies to the maintenance of infrastructure that amunicipality inherits in new subdivisions.

Each of the potential sources of stormwater funding is described briefly below. Of the fivepossibilities, a stormwater utility offers the best long-term option for stability and continuity.Hence, a detailed discussion of utilities is provided in the next section.

General RevenueThis refers to a local government’s annual budget, which is derived from property taxes.Historically, this is how drainage projects were funded. In many municipalities, this is stillthe funding source for drainage programs. Implementing a major capital program cantherefore have a measurable and noticeable impact on property taxes. Furthermore, drainagethen becomes one of a number of competing priorities for Councils to balance. Unless thereis a demonstrated threat to life and property, it can be difficult to gain the necessary politicalsupport to proceed with major capital programs.

Development Cost ChargesDevelopment cost charges (DCCs) were introduced by the Provincial Government in the1970s to ensure that new development paid its fair share of the off-site costs required toservice the development. In the case of drainage, it may be many years before a municipalitycollects sufficient money from individual developers to enable a project to proceed. Hence, awatercourse may be subjected to the cumulative adverse effects of erosion and sedimentation.

Specified Area ChargeLocal governments have the option to create Specified Areas for the purpose of recoveringthe cost of providing a specific service. An example would be a Local Initiatives Programfor road and drainage improvements.

Stormwater UtilityThe purpose of any local utility is to provide a self-sustaining source of revenue to fundimplementation of capital and maintenance programs over a multi-year period. BCmunicipalities have historically had both water and sanitary utilities. Funding is raisedthrough a user fee.

Although stormwater utilities are often discussed in BC, there has been a lack of will at thelocal government level to implement them. In recent years, however, several municipalities(notably the cities of Surrey and North Vancouver) have broadened the scope of their sanitarysewer utilities to encompass drainage. This has enabled those municipalities to proceed withmajor capital projects.

Washington State municipalities, including Bellingham and Bellevue, have adoptedstormwater utilities. The Bellevue utility was one of the first such utilities in North America.

Senior GovernmentsHistorically, senior governments have not provided funding for drainage in BC, other than theFraser River dyking program and flood disaster response programs. The FederalGovernment’s newly created Green Municipal Enabling Fund is the first opportunity for


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some local governments to access funding for stormwater management in the suburbanregions.


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10. 5 Setting Up a Stormwater UtilityA stormwater (or drainage) utility may be defined as a self-liquidating entity that has afocused purpose for stable and dedicated funding for surface water quantity and qualitymanagement, operations and maintenance, rehabilitation and enhancements.

The information presented in this section is included courtesy of the District of Maple Ridge.It is adapted from a staff presentation to Council in 2001.

Legislative AuthorityA stormwater utility is permitted under the following sections of the Local Government Act:

� Section 363.(1) – A Council may, by bylaw, impose a fee or charge payable inrespect of full or part of a service of the municipality

� Section 517.(1) – Subject to the specific limitations and conditions established byor under this Act, a municipality may operate any service that the Councilconsiders necessary or desirable for all or part of the municipality

� Section 518.(1) – A bylaw under this Part may (a) establish different classes ofpersons, places, activities or things, and (b) make different provisions fordifferent classes and for different areas of the municipality

Scope of a UtilityStormwater utilities typically include a network of pipes, streams, ponds and lakes fordetention and water quality control. The utility is set up to address both:

� the built stormwater system – pipes, pump stations, outfalls� the natural stormwater system – creeks and streams

Its purposes are primarily flood protection, erosion control and environmental protection.

Addressing Public ConcernsPublic concerns that a utility would typically address include:

� flooding� water pollution� property damage� stream erosion� habitat impacts� wetland acquisition� stormwater detention

Utility FocusTypical programs for a stormwater utility include:

� water quality control, including education� operations and maintenance� development regulation� capital improvements

Objectives and ServicesStormwater quality protection objectives may include:

� water quality for safety and enjoyment of residents� preservation of aquatic and wildlife habitat

Particular services a utility may provide include:

� 24-hour emergency response for flooding and hazardous spills� residential and other built connections to the utility’s drainage system� erosion control� operation and maintenance of drainage systems� flood warning systems� water quality and environmental monitoring


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Financing PrinciplesFinancing principles for utilities include:

� user fees (and demand management)� charge based on benefits or cost of service

The total revenue is derived from utility rates/fees as well as DCCs.

Benefits of a Stormwater UtilityBenefits fall into two categories: environmental and functional.

The environmental benefits are:

� habitat protection� habitat rehabilitation� ecological enhancement

The functional benefits include:

� stable and dedicated funding for long-term initiatives and public goals� equitable distribution of costs to users� ability to finance and implement innovative technologies and solutions� ability to upgrade systems and eliminate deficiencies� long-term strategic planning for sustainability and flexibility

Challenges for a UtilityIn setting up a utility, challenges that need to be overcome include:

� perception of ‘inflexible’ funds� perception of another tax� not eligible for Home Owners Grant� service may not always be transparent� user ability to pay

Determining the PurposeIn forming a utility, a major consideration is deciding its purpose(s). The choices include:

� flood control� water quality protection and pollution prevention� natural stream and water body management� erosion and sedimentation control� combined sewers for sanitary and storm drainage

Revenue and BillingDeciding on the utility purpose(s) leads to revenue and billing considerations:

� Initial revenue requirements –� Which programs are to be undertaken first and which will be phased in?� Where will the working capital for starting up the utility come from?

� Billing structure and mechanism –� What are the classifications or rates?� Can the existing billing system accommodate this?

Timing and RatesQuestions related to implementation that must be addressed include:

� Timing – It usually takes two to three years to start up a utility – what is the long-term financial plan for the utility?

� Initial rates – What is the appropriate level, and phase in?

Stormwater Utility RatesExamples of annual stormwater utility rates include: City of Surrey ($55+); City of Bellevue,Washington State ($130+), and Snohomish County, Washington State ($30+).


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10.6 Regional ApproachLocal government has responsibility for land use decisions. Local government is alsoresponsible for protection of property. Because it is better positioned to protect theenvironment, local government is now being called on to play a primary role in aquatichabitat protection, restoration and management. During this period of transition, however,there is uncertainty as to what this change means, and who pays. BC can learn from theWashington State experience.

Cross-Jurisdictional Funding of Watershed Action PlansWatercourses cross local government boundaries. This raises a host of inter-jurisdictionalissues. Commencing in 1994, the thirty-nine cities in King County, Washington State, havebeen attempting to address watershed management issues (flooding, fish habitat and waterquality) through Inter-Local Agreements. Notable accomplishments to date include:

� trust has been built incrementally� Watershed Forums have been created � Regional Funding Principles have been adopted (1997)� policy guidelines have been defined for a co-operative approach

Lessons that can be learned from the King County experience are distilled as follows:

� need regional decision-making for investments� need regional funding� need multi-level forums

While a voluntary approach in King County has been successful at developing consensus andcommunity priorities, it has failed to deliver:

� regional funding � certainty - due to the governance issue� ability to do new regional projects

Based on the King County experience, ensuring success at the watershed scale means theremust be an over-arching decision authority in place plus senior government funding.

Other British Columbia Experience Three regional districts (Greater Vancouver, Capital Region, and Nanaimo) have developedor are in the process of developing regional approaches to ensure consistency in municipalstormwater management strategies. These are a component of Liquid Waste ManagementPlans (LWMPs). However, there is no precedent in British Columbia for inter-municipalfunding of implementation plans for cross-boundary watershed protection or restoration.

Quasi-precedents for cross-jurisdictional stormwater funding in British Columbia may befound in regional water supply and wastewater treatment systems. Typically, this means thatmember municipalities have designated responsibility to regional districts (through ‘letterspatent’) for these functions. Based on a cost sharing formula, the municipalities contributefunding for capital improvements and operation and maintenance of the regional function.This arrangement offers a possible template for a regional approach to stormwater funding.

Chapter Eleven

11.1 Developing a Shared Vision� Benchmarking a Watershed Vision to an Official Community Plan� How Do We Get There?� Providing a Clear Picture of the Watershed Vision

11.2 Overcoming Barriers to Implementation� Barriers to Change in Local Government� Guiding Principles to Overcome Barriers� Gaining Political Commitment through Consensus-Building

11.3 Moving from Planning to Action� Critical Success Factors for Moving from Planning to Action� Accomplishing Institutional Change

11.4 Translating a Shared Vision into Action� A Three-Track Process� Stakeholder Involvement

11.5 Using Working Sessions to Build Consensus� Consensus Explained� How Adults Take Up New Ideas� Working Sessions Result in Knowledge Transfer

Building Consensus and Implementing Change



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11.6 Administering an Action Plan� Track #3 – Finance and Administration� Constant Improvement

11.7 Defining Roles and Aligning Responsibilities� Local Government� Senior Levels of Government� The Private Sector� The Public� Inter-Governmental Co-operation Agreements

11.8 Creating Change Through Public Communication� Communicating the Need for Change� Ingredients to Build Consensus


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11.1 Developing a Shared VisionSuccessful implementation of Integrated Stormwater Management Plans (ISMPs) depends onhaving the support of the community. If the public and elected officials have a shared visionfor integrating stormwater management with land use planning, funding and implementationare far more likely to follow.

With participation of the regulatory agencies in the visioning process, senior governmentsare far more likely to support a local government’s efforts and less likely to imposeburdensome requirements.

Benchmarking a Watershed Vision to an Official Community PlanAn Official Community Plan (OCP) presents a vision of the future, and provides abenchmark for referencing the goals and objectives of the stormwater planning process. AnOCP is an official statement of policy and reflects community values. A representative OCPVision Statement is presented below:

“The City shares the goal of sustainable development, and believesthat good ecology is fundamental to…preserving the City’s vision of

an urban community in a sea of green”

Source: 1990 City of Chilliwack OCP

The purpose of an ISMP is to translate the OCP vision into a stewardship-based watershedvision. Stream stewardship is the act of taking responsibility for the well-being of streamsand stream corridors, and carrying out works to protect or restore that well-being.

How Do We Get There?Protecting property, accommodating growth and development and sustaining natural systemsis a balancing act. Achieving this balance through an ISMP process involves a 3-stepprocess:

� first, there has to be a perceived need� this then establishes the goals in developing a strategy� finally, implementation requires public support in order to generate political

action

To be effective, a watershed (or catchment) strategy must be based on a clear definition ofshared goals and realistic expectations for achieving them.

Critical Success Factors for Developing a Watershed VisionFundamental ingredients to build consensus and ultimately implement a watershed vision arelisted below:

� Achievable and Affordable Goals - Apply a science-based approach tocreate a shared vision for improving the health of individual watersheds overtime.

� Participatory Decision Process - Build stakeholder consensus andsupport for implementing change, and agree on expectations and performancetargets.

� Political Commitment – Secure political agreement on the need for action.

Long-Term Vision and Priorities for ActionA shared long-term vision is required to focus effort. This vision provides a context for allplanning, data collection, capital expenditures and regulatory changes that result from anISMP.

Prioritizing goals and actions (through consensus) provides a roadmap for moving towardsthe long-term vision.


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Providing a Clear Picture of the Watershed Vision

Figure 11-1 provides a picture of the shared 50-year vision for the Como Creek watershed inthe City of Coquitlam. This watershed comprises an upper benchland and a lowerfloodplain. There has been a history of flooding problems in the lowlands. A series ofdrainage reports on the lowland problems had been completed over a 25-year period.However, the overall picture provided by those reports was complex and confusing.

The first priority was to develop a common understanding of the nature of the problem.Upstream urbanization in the Como Creek watershed has resulted in more surface runoff,flow is concentrated at a single drainage outlet, and the Trans-Canada Highway acts as abarrier that restricts the rate of outflow from the watershed. Once the nature of the problemwas understood by all participants, it quickly became possible to reach consensus on how toprovide flood relief and restore aquatic habitat.

Figure 11-1 presents the three elements of the Como Watershed Vision, and three supportingactions for one of those elements.

Figure 11-1


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11.2 Overcoming Barriers to ImplementationEffective integration of engineering, planning and environmental solutions is often discussedbut rarely achieved. Figure 11-2 on the next page illustrates the results of an Americansurvey that identified the top ten reasons that decisions fail. The first four relate directly tohuman behaviour, with the #1 reason being the lack of a ‘decision process’.

Barriers to Change in Local GovernmentIt has been recognized that dealing with stormwater and aquatic habitat issues must beintegrated with decisions about land use change. But making this a reality is easier said thandone. There are a number of barriers that make bringing about change difficult, including:

� Lack of a Champion� Lack of Trust (“Why should I believe you?”)

� Liability (“What if it doesn’t work?”)

� Access to Resources (staff and money)

� Uncertainty About How to Go Forward

� Attitudinal (“Who cares?” or “Why change?”)

� Jurisdictional Conflicts (internal and external)

� Educational (i.e. how new ideas are accepted)

Guiding Principles to Overcome BarriersThe risks and the impacts have become drivers for change in the way stormwater is managedin BC. Once a champion is identified to provide leadership, following these principles willcreate the momentum needed to build support to implement change:

� Build Trust� Solve the Right Problem� Avoid Useless Data� Manage Risk and Liability� Put Interest and Values First� Avoid Advocacy Positions� Find Lowest Cost Solution� Track Progress� Ensure Effective Communication� Learn from Mistakes� Share Lessons Learned

Gaining Political Commitment through Consensus-BuildingBringing about voluntary change by local government involves a systematic process assummarized below:

� Demonstrate the Need for Action� Integrate Diverse Perspectives� Align Roles and Responsibilities� Communicate with Stakeholders� Partner with Regulatory Agencies� Implement a Participatory Process

Technical people have to demonstrate cost-effectiveness in order to transform politicalacceptability into the political will needed to implement change and spend money.


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1. Lack of Decision Process

2. Lack of Leadership/Vision

3. Lack of Commitment

4. Wrong Stakeholders

5. Inadequate Information

6. Wrong Problem

7. Politics

8. Insufficient Time

9. Corporate Culture

10. Risk Aversion

Figure 11-2 Most Decisions Fail Because of Organizational Rather than Analytical Issues


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11.3 Moving From Planning To ActionThe history of drainage is that floods occur, post-mortem reports are written, the sense ofurgency wanes, and there is inaction until the next flood serves as a reminder that the issueremains unresolved. This historical reality provides a frame of reference for overcoming thechallenges involved in implementing integrated solutions.

Critical Success Factors for Moving from Planning to ActionBridging the gap between planning and action requires that three critical success factors be inalignment:

� Political Commitment – to take action to integrate stormwatermanagement with land use planning

� A Champion Within Local Government – to provide energy andorganizational drive and to stimulate willingness to change

� Trust – between individuals, and between levels of government

Section 11.6 provides guidance for organizing an administrative system and financingstrategy for moving from planning to action. The roles and responsibilities of various levelsof government, the private sector and the public are defined in Section 11.7.

Integration of OCP and LWMP ProcessesThe Official Community Planning process is planner-led. The Liquid Waste ManagementPlanning process is engineer-led. Yet the two processes are highly related, and are in factcomplementary. This underscores the need for integration to breakdown inter-departmentalbarriers.

Accomplishing Institutional ChangeRisk aversion is usually given as the reason that governments are reluctant to embraceinnovation and integrated solutions. However, as demonstrated by Figure 11-2, the #1organizational factor that results in failure to move from planning to action is the lack of adecision process. Understanding this reality leads to the following principles:

� Principle #1: Melt the Opposition – Obtain commitment from keystakeholders to support change (i.e. new values and beliefs).

� Principle #2: Implement the Change – A good idea is immediate,but preparation for implementation can take 5 to 10 years. Change will then takeplace quickly (e.g. within 6 months).

� Principle #3: Re-Freeze – Reinforce new values and institutionalize thechange.

Principle #1 can only be accomplished through a participatory and collaborative decisionprocess for building consensus as explained in the following sections. A desired outcome isto align the roles and responsibilities of all levels of government to achieve a shared goal.

Organizational RequirementsA lead organization is needed for watershed and drainage catchment planning. The range ofpossibilities is summarized as follows:

� local government for larger municipalities

� regional districts for smaller municipalities and rural areas

� First Nations on large reserve lands

Other levels of government and stakeholders (besides the lead organization) will beintegrated through the consensus process that is discussed next.

A key to future success in ISMP implementation is the ability of departments tocommunicate with other departments and disciplines to achieve effective changes in the waylocal governments plan and design neighbourhoods.


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11.4 Translating a Shared Vision into Action

A Three-Track ProcessISMP development and implementation requires a three-track process, where technicalanalysis feeds into working sessions with all stakeholders, and a financing and administrationplan is built to support implementation.

� Track #1: Technical Products – Identify watershed characteristics,problems and potential management solutions through a technical analysisprocess that combines the analytical skills and tools from engineering, planningand ecology. Assess strategies and model implementation scenarios. Computersimulation may help identify what is achievable.

� Track #2: Working Sessions – Present and refine technical products ata series of workshops and working sessions with all stakeholders. Thesesessions will improve understanding and enable informed, consensus-baseddecision making regarding a shared, long-term watershed vision, appropriatestrategies for achieving the vision and roles and responsibilities forimplementation.

� Track #3: Finance and Administration – Organize anadministrative system and financial vehicle that is appropriate to the scale of thestormwater management program. In some rural areas, regulation may suffice onits own. In urbanizing areas, a means of collecting and organizing for capitalinvestment and operations will likely be necessary.

Adaptive ProcessIt is important for all stakeholders to be working towards the same long-term vision (e.g. 50years) at all stages of the process. The three tracks of effort must work within an adaptiveframework to constantly measure success (the effectiveness of technical solutions andprogress towards the long-term vision) and optimize management actions.

Integration of PerspectivesThe goal and the challenge is to achieve full integration of the engineering, planning andecological perspectives. The ISMP must be based on science, but it must also achieveconsensus among stakeholders at many levels. As a result, Tracks #1 and #2 must happen inparallel to both inform and balance the many perspectives at the table.

Technical analysis in isolation of stakeholder understanding will not survive the agency andpolitical approval processes. Conversely, stakeholder decisions that are made on technicallyfaulty information are at high risk of failure. However, when the two tracks of technicalproducts and working sessions are used together simultaneously, both processes lead tobetter understanding and better decisions with more stakeholder support.

The remainder of this section outlines how Tracks #1 and #2 work together; Track #3 isdiscussed further in Section 11-6.

First Priority is to Understand the WatershedHaving an on-the-ground understanding of a watershed is a core critical success factor.Examples of technical products (Track #1) were introduced in Chapter 9 and include:

� Watershed Base Map - the first building block� Watershed Issues Summary - where and what are the identified problems� Sensitive Ecosystem Inventory - what is to be protected� Concurrent Rainfall and Streamflow Data - how the watershed responds to rainfall� Drainage System Inventory - how the conveyance system functions� Land Use Map - what are the existing and future generators of runoff� Soil Infiltration Map – where might infiltration be feasible


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Stakeholder InvolvementThere are three tiers of stakeholders:

� Group One: ISMP Steering Committee – comprises inter-departmentalrepresentatives from planning, engineering, development services, parks,environmental planning and finance

� Group Two: ISMP Focus Group – comprises representatives from federal andprovincial agencies as well as from key community advisory groups (e.g.streamkeepers, neighbourhood associations and local business associations)

� Group Three: Watershed Forum – the general public

Working sessions should typically involve both the Steering Committee and the FocusGroup. The objective in having the agencies and others participate in a learning environmentis to obtain early buy-in to solutions and strategies. Some technical workshops may involveonly the Steering Committee where the focus is to be on contract, property or financialissues.

Watershed ForumGroup Three would be only involved at events where the purpose is essentially informationpresentation, with limited discussion. The size of Group Three would make it difficult forinformal discussion. A more structured approach involving questionnaires and small groupbreakout sessions could make Group Three consultation more focused and productive.

Collaborative ProcessTable 11-1 on the next page outlines how Tracks #1 and #2 work together to achieveunderstanding of and commitment to the ISMP process.


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Track #1 – Technical Products

Step 1 - Basic Mapping and Problem IdentificationMap ecological, drainage and land use information to identify at-risk catchments whereland use change:

� threatens high-value ecological resources� could cause unacceptable drainage problems.

(refer to Chapter 5)

Step 2A - Performance targets and site design criteria for achieving shared goals*Analyze site-specific rainfall data to set performance targets for rainfall capture, runoff controland flood risk management. Translate performance targets into design criteria that can beapplied at the site level (refer to Chapter 6).

*set targets and design criteria for priority catchments first

Step 2B - Alternative strategies for achieving these targets and design criteriaChapters 7 and 8 provide guidance for selecting appropriate strategies at the land use andcommunity planning level, and at the site design level (including specific examples).

Step 3A - Implementation and monitoring of demonstration projects in at-risk catchmentsTest the effectiveness (and affordability) of various site design options, while taking immediateaction to achieve priority goals.

Step 3B - Evaluation of local development standards and regulationsIdentify development standards and regulations that impede better stormwater managementand land development practices (e.g. rainfall capture at the source, narrow roads).

Step 4 - Monitoring of progress towards performance targets and the long-term visionRequires strategic collection of data to track indicators of success and enable ongoingassessment of progress towards performance targets and the long-term vision.

Track #2 – Deliverables for Working Sessions

Step 1 - Shared Vision, Goals, and PrioritiesDevelop a long-term vision that is shared by all stakeholders, and establish the key goals andobjectives that correspond to this vision.

Achieve consensus on a priority at-risk catchment to focus early action, as well as the nextpriorities for action.

Step 2 – Strategies for achieving performance targets* and long-term visionAchieve consensus on the strategies that would be most practical and achievable in the contextof:

� Local conditions� The needs and interests of all stakeholders

*appropriate strategies for achieving performance targets should be defined in priority at-risk catchmentsfirst

Step 3 - Changes to local development standards and regulations:� to require that development and re-development projects incorporate source

control (recommend the most effective and affordable options)� to remove regulatory barriers to better stormwater management and land

development practices

Change must occur through consultation with all stakeholders, particularly developers andlandowners.

Step 4 - Optimize stormwater management actionsImprove community planning and site design practices based on stakeholder response to theongoing assessment process.

Stakeholder participation is key to defining success and developing indicators of success.

Table 11-1 Adaptive and Collaborative Process for Translating a Shared Vision into Action


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11.5 Using Working Sessions to Build Consensus

Consensus ExplainedThere are usually complex trade-offs involved in choosing the appropriate integratedsolution. Many of the decisions about choice of solution require judgement – about publicvalues and priorities, about the pace of change, and even about environmental conditionsbased on the currently available scientific information. Choices, especially, involve balanceamong competing objectives.

The best tool to find this balance is consensus. The word consensus is defined in manydifferent ways, but a working definition can be ‘the lack of violent objection’.

The same values might be given different emphasis by different stakeholders – engineering,operations, planning, fisheries, land use development, parks, recreation, homeowners,highways or stewardship groups. The differences in values and emphasis usually stem fromwhat we have been taught and what we have experienced. Consensus is important because itincorporates relevant education and experience from all disciplines and all experience at thetable.

How Adults Take Up New Ideas and ApproachesFigure 11-3 illustrates how education leads to implementation. The Figure elements can beread in both the horizontal and vertical directions. Education leads to shared, achievablegoals. In turn, these goals culminate in action and implementation.

An understanding of how adults learn can help to explain why and how new ideas areaccepted, and why some adults accept them faster than others. Learning is a gradual process.Adults take in new information, reflect on it, blend it with their own experience, test it, andeventually apply it in making decisions.

The differences in the way people accept new ideas, and the fact that learning is a gradualprocess, underscores the necessity and value of workshops and working sessions. Properlystructured, they break down barriers, promote communication and transfer of knowledge, andmake it possible to bring people along at different rates of acceptance.

Figure 11-3


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Working Sessions Result in Knowledge TransferExamples of themes for working sessions to develop consensus around watershed objectivesare listed below. Each session would have a product or expected outcome to maintain thefocus. Each product is a building block in the broader ISMP process. Since the sessions areinteractive, they also provide an effective feedback loop to evaluate the process itself. Aswell, working sessions facilitate incremental buy-in to a shared vision.

EXAMPLE SESSION THEME SESSION PURPOSE

Project Initiation and Chartering Clarify goals, expectations anddeliverables

Watershed Issues Workshop Define issues, needs and driving forces

Hydrology Workshop Develop a common understanding ofissues

Fisheries and Ecology Workshop Confirm habitat values and limitations

Watershed Vision Workshop Evaluate performance targets

BMP Workshop Focus on green infrastructure costs andbenefits

Strategy Development Workshop Develop framework for the integrated plan

Elements of an Integrated Plan - I Brainstorm pros and cons of the planelements

Elements of an Integrated Plan - 2 Reach consensus on the plan elements

Regulatory and Communications Plan Address regulatory and public awarenessroles

Implementation Plan Finalize plan details

This list is only intended to provide a starting point for customizing an appropriatestakeholder program for individual watersheds or catchments. Based on experience, aminimum of four sessions is usually needed for participants to become comfortable witheach other and reach consensus.

Structure and DocumentationThe agenda for each working session should state the purpose in meeting, define a set ofobjectives, and indicate the desired outcome. The session should comprise a series of shortpresentations of the relevant technical analyses, with each presentation segment followed bya question and discussion period. A facilitator can be useful to keep the sessions focused onthe desired outcome. Note that:

� Structure is provided by a set of presentation slides that guide the discussion.These slides can then become part of the record of the session.

� Focus is provided by means of presentation material and/or drawings (i.e.technical products from Track #1).

� Documentation is provided through a short-form and succinct session summarythat can be included as an appendix to the ISMP.

Working sessions are an effective forum for sharing information, experience and knowledge.Structured sessions foster a learning environment that results in improved communicationthat in turn leads to enhanced understanding and acceptance.


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11.6 Administering an Action PlanDeveloping an ISMP is an intensive and extensive process. There is a lot for the participantsto remember. The information would be overwhelming if conveyed in its entirety to electedofficials. To make decisions related to ISMP implementation, elected officials need relevantinformation in a concise format.

Track #3 - Finance and AdministrationSection 11.4 outlined a three-track approach to building, planning and implementingintegrated stormwater management solutions. Table 11-2 is a checklist that summarizes thescope of what is involved in Track #3 - Finance and Administration. The focus is on creatingan action plan that identifies the specific activities or projects that need to be completed.The scope of a watershed-specific action plan is summarized below.

Scope of an Action PlanFrom an elected official perspective, the key deliverable for any watershed or catchmentplanning initiative is the action plan that defines the specific activities required to achieve thelong-term vision. It is important to provide the following information for each proposedactivity:

� Time-frame for implementation� Management objectives� Priority (relative to other action items)� Who takes the lead role?� Estimated cost and financing strategy

An action plan should cover the 5-year, 20-year and 50-year implementation timeframes. Toillustrate this, an Action Plan that resulted from the City of Coquitlam’s Como Creek ISMPis presented in Table 11-3.

Table 11-2 Finance and Administration Protocol forImplementing an Action Plan

1. Review existing administrative systems to identify potential departmentalorganization for stormwater management.

2. Create a summary Action Plan that identifies the actions or projects that needto be completed.

3. Select or create a lead department for integrated stormwater management.

4. Clearly identify what actions are to be led by which department and relatedbudget requirements.

5. Identify the capital and operating financing required, and relate to scheduleand other priorities.

6. Review fundraising options and implications.

7. Obtain political and public review in draft form.

8. Refine the Action Plan.

9. Formalize the Action Plan.

10. Consider and adopt the Action Plan.


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Constant ImprovementAction plans should be long-term, corresponding to the time frame of the watershed vision,but must be revisited periodically (e.g. every 5 years) and updated based on the ongoingassessment of progress towards the shared vision. This is the foundation of an adaptiveapproach.

The 50-year vision reflects the long time frame required for change. Over time, as betterdevelopment practices evolve and as a watershed is gradually retrofitted with rainfall captureand runoff control measures, it will be important to monitor the success of watershedprotection and restoration. This is essential for the adaptive approach to work.

The ongoing assessment process will provide better understanding of the policy, science andsite design aspects of integrated stormwater management. This will enable constantimprovement of integrated solutions.


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Time-frame Action Items Management Objective Lead Role Budget

Short-term Flood Risk Management Provide Immediate Flood ReliefShort-term(0-5 years)

Improve Lowlands Drainage Systema) Remove Booth Creek channel constrictions at and below Lucille Starr Way.b) Expand the rainfall and streamflow monitoring network.c) Build a calibrated hydraulic model for the Lowlands drainage system.d) Upgrade the Booth/Popeye Inter-Watershed Connection.e) Implement the Inter-Watershed Flow Control System at theTrans-Canada Highway.f) Create a separate drainage outlet for Booth Creek under the Lougheed Highway.

a) Eliminate chronic flood overflows onto Schoolhouse Street.b) Monitor watershed changes over time; provide the data needed to calibrate models.c) Develop operating rules for effective flow management in the Lowlands.d) Transfer peak flows and eventually restore two separate sub-watersheds.e) Improve capacity of Como Creek system to reduce risk of flooding above the highways.f) Improve capacity of Como Creek system to reduce flooding; create fish habitat.

OperationsOperationsOperationsOperationsOperationsOperations

Short-term(0-5 years)

Upgrade High-Risk Culverts and Provide Bedload Interceptiona) Upgrade the Como Creek culvert at Rochester Ave. and provide bedload interception.b) Upgrade the Booth Creek culvert at Austin Ave. and provide bedload interception.c) Upgrade the Como Creek culvert at Austin Ave. and provide bedload interception.

a) Reduce risk of localized flooding and potential road washout; reduce downstream deposition.b) Reduce risk of localized flooding and potential road washout; reduce downstream deposition.c) Reduce risk of localized flooding and potential road washout; reduce downstream deposition.

OperationsOperationsOperations


Provide Community Storage Facilitiesa) Implement the Como Lake Storage and Flow Regulation Modifications.b) Construct Popeye Detention Pond on BC Hydro Site.

a) Reduce erosion in Como Creek Ravine; reduce downstream deposition and flooding risk.b) Improve the effectiveness of the Booth/Popeye inter-watershed connection.


Long-Term Watershed Restoration Eventually Restore the Health of the WatershedShort-term(0-5 years)

Identify Targets & Design Options for Source Storage and Infiltrationa) Implement the Casey Place Bedload Management Plan.b) Build a calibrated hydrology model for the Como Creek watershed.c) Complete a hydrogeologic investigation of the Como Creek watershed.d) Implement and monitor source storage and infiltration pilot projects on public works.e) Establish a consultation process with landowners and the development community.f) Create an on-line technical manual of options for on-lot storage and infiltration.

a) Reduce bedload deposition and flooding risk in the Lowlands.b) Establish target conditions for long-term watershed restoration; optimize management solutions.c) Identify areas within the watershed that are suitable for infiltration at the source.d) Identify appropriate source storage and infiltration targets and identify the best design options.e) Identify design options acceptable to landowners and developers.f) Make design details for source storage retrofit readily available.

OperationsOperationsOperationsOperationsDev. ServicesDev. Services

Table 11- 3 Implementation Actions for the Como Creek ISMP Page 1 of 2


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Time-frame Action Items Management Objective Lead Role Budget


Build Support for Watershed Retrofits Through Educationa) Provide a self-guided training program including tours, fact sheets, videos and website information.b) Offer training workshops and seminars to the development community.c) Work with other agencies to design a one-day watershed training and certification program.d) Require that all public works staff and contractors become watershed-certified.

a) Educate development community, city staff and public about the need for changes in development practices.b) Educate development community about how to implement changes in development practices.c) Educate city staff about need for changes in development practices and how to implement them.d) Ensure that City staff can lead by example.

Parks & EnvParks & EnvParks & EnvOperations


Change Development Regulations to Ensure that Source StorageRetrofit will Occur in Conjunction with Future Re-developmenta) Remove barriers to source storage and infiltration in existing development regulations.b) Incorporate the most appropriate targets and design options into the Engineering Standards.c) Incorporate the new Engineering Standards into the Subdivision Bylaw, Building Bylaw, Zoning

Bylaw and Development Permit Guidelines.

a) Ensure that the regulatory framework does not discourage source storage retrofit.b) Ensure that the watershed will be restored through source storage retrofit as re-development occurs.c) Ensure that the watershed will be restored through source storage retrofit as re-development occurs.

Dev ServicesOperationsDev Services

Short-term(0-5 years )

Demonstrate a Commitment to Watershed Restorationa) Implement a water quality source control program in the Lowlands.b) Implement the East Surge Channel Habitat Bank.

a) Improve water quality in the Lowlands by eliminating sources of leachate.b) Create new fish habitat in the Como Creek system; provide compensation for future projects in the watershed.


Medium-term(5-20 years)

Facilitate the Implementation of Source Storage Retrofit Strategya) Provide expedited approvals on private sector projects that implement source storage.b) Implement a composting program to provide low-cost organic matter for absorbent soils.c) Implement a program for bulk purchase and resale of storage and infiltration products.d) Continuously monitor rainfall-runoff response and other indicators of watershed health.

a) Facilitate approval process for re-development projects that implement source storage and infiltration.b) Facilitate the procurement of absorbent soils needed to provide infiltration at the source.c) Facilitate the procurement of materials needed to retrofit individual re-development projects.d) Assess the effectiveness of the source storage retrofit strategy in achieving watershed restoration.

Dev ServicesParks & EnvOperationsOperations

Medium-term(5-20 years)

Restore the Natural Watershed Drainage Patterna) Create a new drainage outlet at the highways for the Booth/Popeye sub-watershed. a) Achieve the overall vision for two separate sub-watersheds, (Como/MacDonald and Booth/Popeye). Operations

Long-term(20-50 years)

Restore Watercourses to Their Natural Statea) Restore the Popeye Creek stream corridor between Brunette and Lougheed Highway.b) Daylight the piped section of Booth Creek between Sheridan and Myrnam.c) Daylight the piped section of Como Creek below Como Lake.d) Daylight the piped section of Booth Creek below Foster.e) Daylight the piped section of Como Creek below Rochester.

a) Restore healthy aquatic and riparian ecosystems in the Popeye Creek system.b) Restore Booth Creek to its natural state; create a neighbourhood amenity.c) Restore Como Creek to its natural state; create a neighbourhood amenity.d) Restore Booth Creek to its natural state; create a neighbourhood amenity.e) Restore Como Creek to its natural state; create a neighbourhood amenity.

OperationsOperationsOperationsOperationsOperations

Table 11- 3 Implementation Actions for the Como Creek ISMP Page 2 of 2


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11.7 Defining Roles and Aligning ResponsibilitiesOnce there is agreement to move from planning to action, the next step is to define roles andalign responsibilities, both for individuals and levels of government.

Local GovernmentLocal governments are the primary players. They control land use decisions, have acomprehensive mandate and are directly accountable to local citizens. Their keyresponsibilities include:

� Supporting stormwater management objectives through land use planning andgrowth management.

� Changing municipal development standards and regulations (e.g. engineeringstandards, zoning bylaws, development permit guidelines, etc.) to enable lowimpact development and stormwater management.

� Making details of changes readily available to the development community.

� Financing capital works projects (e.g. drainage system improvements,community detention).

� Taking a leadership role by implementing demonstration projects for rainfallcapture best management practices (BMPs) on public works.

� Facilitating the procurement of products needed for source-control BMPs.

Senior Levels of GovernmentKey responsibilities include:

� Providing financial support through provincial and federal programs.

� Providing technical support as required (e.g. the Stewardship series ofdocuments).

� Streamlining the agency approval process.

� Facilitating integration where stormwater management issues cross jurisdictionalboundaries.

The Private SectorThe key role for developers is to incorporate rainfall capture BMPs into development and re-development projects. Developers are ultimately responsible for on-the-groundimplementation of low impact development and stormwater management practices at the sitelevel. Developers can also play a key role in finding creative and affordable solutions toachieve stormwater performance targets.

The PublicBuilding public support through education is key. This public support translates intopolitical will for change. An educated public can stimulate action. All levels of governmenthave a role in building public support through stormwater education initiatives.


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Inter-Governmental Co-operation AgreementsInter-Governmental Co-operation Agreements (IGCA) provide a vehicle for aligningresponsibilities among all levels of government. The intent of an IGCA is to bring all partieswhich share a goal – or who are essential players in achieving other jurisdictions’ goals –together so that they can apply their various mandates, resources, and capabilities to do thejob both efficiently and effectively for all concerned. Important principles and factors toconsider in developing such agreements are listed below:

1. Define Reasons for Intergovernmental Collaboration - Purpose,topic, scope, benefits to be gained (in ‘whereas’ statements).

2. Recognition of Roles and Responsibilities - By definition, collaborationis not about hierarchical power-based relationships, but partnerships irrespective of whohas power. Acknowledge independence (with respect to constituency and relatedaccountabilities) and then deal with collaboration among independent parties acting withreference to mutual interests.

3. Principles and points for consideration in collaboration -

� commitment to action with reference to jurisdictional roles, responsibilities andaccountability (clarity on who does what, where, when)

� partnerships based on strengths and capabilities (co-operation and harmonizationwith respect to legislation, regulations, policies, programs and projects)

� consultation on and confirmation of resources needed to do job (impactassessment of costs and benefits and their incidence and resolution of potentialissues regarding funding, liability and resources)

� flexibility (to adapt to conditions that may arise in the administration of acollaborative initiative)

� notification and consultation (to address any changes that may emerge)

� information sharing

� dispute resolution

� involvement of civil society (who, how, when, by whom)

� implementation sub-agreements (to address specific topics or actions)

� administration of agreement (committee(s) and review process to monitorperformance and renew, revise or refine agreement(s))

Local governments have now been unequivocally called on by senior governments and thepublic to protect fish habitat in British Columbia. Principle-based agreements will receiveincreasing attention as a key ingredient in achieving multi-jurisdictional communitydevelopment and stream health protection objectives.


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11.8 Creating Change through Public CommunicationAn ISMP may identify required changes to land use regulations in order to implement astormwater strategy. But public support and the political system will determine the timing andphasing of those changes.

Furthermore, public attitudes and the ability of the development community to adapt will setthe pace of change. The pace can be accelerated by intensive public awareness andinformation campaigns. Accordingly, a communications strategy is an essential element ofan ISMP. Such a strategy starts by determining what type of information and training areneeded to support the associated Land Development Action Plan.

Communicating the Need for ChangeOnce BMPs that are appropriate for a catchment have been selected by consensus, and theirtarget areas identified, it is natural to assume that the ‘job is done’. Although ISMPdevelopment may be largely complete, the job of protection and restoration has just begun.Table 11-4 presents guidelines for creating change through public communication to sustainthese protection and restoration efforts.

Initial flood risk management may be accomplished largely by government capital projects.However, the long-range reduction of environmental risk in a catchment will require apermanent change in the way that land is developed and/or re-developed. To accomplish thisrequires fundamental changes in development, construction and operations standards.

This can only be achieved if there is a broad understanding, within the development communityin particular, and the public in general, about best management practices – what they are, whythey are needed and how they can be practically accomplished. To create this fundamentalchange requires reaching a large number of people, many of whom may not be a motivatedaudience.

Table 11-4 Creating Change Through Public Communication

� There are many different audiences (e.g. politicians, various disciplinesof professionals and scientists, students of different levels, volunteergroups, homeowners, construction supervisors and machine operators,builders and labourers). Education materials must be appropriate foreach audience, in terms of their prior knowledge and their learning level.Educators must understand the audience, and begin at their level ofunderstanding.

� Different people have different learning styles. Some learn best byseeing, others by hearing, and others still by doing. An educationprogram must therefore target each of these learning styles.

� Most adults will not remember a message until they have heard it atleast three times, presented in three different ways.

� Awareness fades with time, and as new people enter the system. Amessage needs to be repeated to refresh memories, increaseawareness and to reach new participants.

� The choice of educational media should respect the audience’spreferences, time and available technology.

� Motivation is a key to learning. What’s in it for me? When is theteachable moment? For example, in addition to an awarenessworkshop, a bylaw review may create a teachable moment. So might arequirement for a permit.


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Ingredients to Build Consensus

Public awareness will not be changed in a single event. There is an ongoing need for astewardship communication campaign that is designed to reach the spectrum of audiences inthe watershed. This awareness program needs to allow for repetition and reinforcement overtime. A communications campaign needs to draw from the experience of educators. It alsoincludes ingredients of marketing. Both bodies of knowledge support the conceptssummarized in Table 11-5.

Change in behaviour comes hard and slow. But adaptable human behaviour has been thesecret to human success over the millennia. The key to change lies in understanding whychange is necessary.

Effective communication, using a variety of media and a series of events with increasinglevels of detail, is fundamental to implementing watershed stewardship. When one considersactions with a 20-year or 50-year time horizon, a communication plan must provide for rapidadvances in technology, including increased reliance on the Internet. However, the strategymust also consider the role of traditional school and university education, as well as adulteducation and ‘tail-gate’ contractor instruction in creating change.

Table 11-5 Ingredients to Build Consensus

� Respect each other’s objectives and responsibilities.� Use plain English and eliminate jargon.� Create understanding by using practical examples (e.g. flooding hot spots,

developer complaints, Councillor representations, fish kills, etc.).� Focus on problems and solutions, not on personalities.� Target solutions to specific areas; many solutions will work in only part of

the watershed (e.g. infiltration on favourable soils).� Target solutions by timeline; some can be achieved immediately, some

require 20-year or 50-year time horizons.� Set clear priorities as a group, based on need and cost-benefit analysis,

but also on ‘full-cost accounting’ that also recognizes non-monetaryvalues.

� Recognize solutions that overlap jurisdictions or disciplines; use thisprocess as a way to co-ordinate across departments; what can not beachieved by one department may be possible with two or moredepartments working in tandem.

� Give solutions a home; for inter-departmental solutions, it is especiallyimportant to define the sub-tasks and roles that each department willcontribute in detail; otherwise, there is a chance of inertia or duplication ifdepartmental mandates are unclear.

� Focus on what needs to change; watershed management is so broad, itcan feel like everything is being reinvented; focus instead on items thatneed to change; this might mean a series of minor wording changes tobylaws, or relatively minor changes to construction practices that arephased in as the industry is educated to be prepared for them.

STORMWATER PLANNING: A GUIDEBOOK FOR BRITISH COLUMBIABIBLIOGRAPHY MAY 2002

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BC Ministry of Environment, Lands and Parks. 2000. Environmental Trends inBritish Columbia, 2000.http://wlapwww.gov.bc.ca/soerpt/

BC Ministry of Environment, Lands and Parks. 1998. Tackling Non-Point SourcePollution in British Columbia: An Action Plan.http://wlapwww.gov.bc.ca/wat/wq/bmps/npsaction.html

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BC Ministry of Environment, Lands and Parks. 1996. Saanich Inlet Study. SynthesisReport: Technical Version. http://wlapwww.gov.bc.ca/wat/wq/saanich/sissrs.html

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Booth, D. 1991. Urbanization and the Natural Drainage System. Impacts, Solutions,Prognoses. Northwest Environmental Journal 7: 93-118.http://depts.washington.edu/cuwrm/publictn/nwej1991.pdf

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Hartman, G.F., Groot, C., and Northcote, T.G. 2000. The Ball is Not in Our Court. InSustainable Fisheries Management: Pacific Salmon. Edited by E. Eric Knudsen, C.R.Stewart, D.D. MacDonald, J.E. Williams and D.W. Rieser. Lewis Publishers, BocaRaton, FL. pp. 31-49.

Horner, Richard, and May, C. 1998. Watershed Urbanization and the Decline ofSalmon in Puget Sound Streams. In Salmon in the City May 20-21, 1998, MountVernon Washington, Abstracts. Edited by Anonymous. pp. 19-40.

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Kerr Wood Leidal Associates Limited. 2002. Integrated Stormwater ManagementPlanning Terms of Reference Template. Draft Report. Prepared for The GreaterVancouver Regional District. Burnaby, BC.http://www.gvrd.bc.ca/services/sewers/drain/Reports


Levy, D.A., Young, L.U., and Dwernchuk, L.M. 1996. Strait of Georgia FisheriesSustainability Review. Hatfield Consultants. West Vancouver, BC.Lucchetti, G., and Stewart, C. 1998. Lake Washington: Fisheries Impacts andOpportunities. In Salmon in the City May 20-21, 1998, Mount Vernon Washington,Abstracts. Edited by Anonymous. pp. 15-18

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Nehlsen, W. Williams, J.E. and J.A. Lichatowich. 1991. Pacific salmon at acrossroads: stocks at risk from California, Oregon and Washington. Fisheries. Vol 16,No.2 American Fisheries Society. Bethesda, MD. Pp 4-21.

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Precision Identification Biological Consultants. 1998. Volume 3: Wild Endangered,Threatened and Lost Streams of the Lower Fraser Valley – Summary Report, 1997.Department of Fisheries and Oceans, Vancouver, BC. http://www-heb.pac.dfo-mpo.gc.ca/english/publications.htm#Papers

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Reid G., and Michalski, T. 1999. Status of Fish Habitat in East Coast VancouverIsland Watersheds. In At Risk. Proceedings of a Conference on the Biology andManagement of Species at Risk. Edited by L. Darling. BC Ministry of Environment,Lands and Parks, Victoria, BC. pp. 355-367.

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Westwater Research Unit, University of British Columbia. 1997. Water Quality andStormwater Contaminants in the Brunette River Watershed, British Columbia 1994-95. Prepared for Environment Canada. North Vancouver, BC. DOE FRAP 1997-04.

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